# | Rank | Similarity | Title + Abs. | Year | PMID |
|---|---|---|---|---|---|
| 0 | 1 | 2 | 3 | 4 | 5 |
| 9291 | 0 | 0.9969 | Highlights of Streptomyces genetics. Sixty years ago, the actinomycetes, which include members of the genus Streptomyces, with their bacterial cellular dimensions but a mycelial growth habit like fungi, were generally regarded as a possible intermediate group, and virtually nothing was known about their genetics. We now know that they are bacteria, but with many original features. Their genome is linear with a unique mode of replication, not circular like those of nearly all other bacteria. They transfer their chromosome from donor to recipient by a conjugation mechanism, but this is radically different from the E. coli paradigm. They have twice as many genes as a typical rod-shaped bacterium like Escherichia coli or Bacillus subtilis, and the genome typically carries 20 or more gene clusters encoding the biosynthesis of antibiotics and other specialised metabolites, only a small proportion of which are expressed under typical laboratory screening conditions. This means that there is a vast number of potentially valuable compounds to be discovered when these 'sleeping' genes are activated. Streptomyces genetics has revolutionised natural product chemistry by facilitating the analysis of novel biosynthetic steps and has led to the ability to engineer novel biosynthetic pathways and hence 'unnatural natural products', with potential to generate lead compounds for use in the struggle to combat the rise of antimicrobial resistance. | 2019 | 31189905 |
| 8359 | 1 | 0.9969 | Comparative Genomic Analysis of Acanthamoeba Endosymbionts Highlights the Role of Amoebae as a "Melting Pot" Shaping the Rickettsiales Evolution. Amoebae have been considered as a genetic "melting pot" for its symbionts, facilitating genetic exchanges of the bacteria that co-inhabit the same host. To test the "melting pot" hypothesis, we analyzed six genomes of amoeba endosymbionts within Rickettsiales, four of which belong to Holosporaceae family and two to Candidatus Midichloriaceae. For the first time, we identified plasmids in obligate amoeba endosymbionts, which suggests conjugation as a potential mechanism for lateral gene transfers (LGTs) that underpin the "melting pot" hypothesis. We found strong evidence of recent LGTs between the Rickettsiales amoeba endosymbionts, suggesting that the LGTs are continuous and ongoing. In addition, comparative genomic and phylogenomic analyses revealed pervasive and recurrent LGTs between Rickettsiales and distantly related amoeba-associated bacteria throughout the Rickettsiales evolution. Many of these exchanged genes are important for amoeba-symbiont interactions, including genes in transport system, antibiotic resistance, stress response, and bacterial virulence, suggesting that LGTs have played important roles in the adaptation of endosymbionts to their intracellular habitats. Surprisingly, we found little evidence of LGTs between amoebae and their bacterial endosymbionts. Our study strongly supports the "melting pot" hypothesis and highlights the role of amoebae in shaping the Rickettsiales evolution. | 2017 | 29177480 |
| 9341 | 2 | 0.9969 | Horizontal gene transfers in insects. Horizontal gene transfer is the transfer of genetic material across species boundaries. Although horizontal gene transfers are relatively rare in animals, the recent rapid accumulation of genomic data has identified increasing amounts of exogenous DNA inserts in insect genomes. Most of the horizontally acquired sequences appear to be non-functional; however, there is growing evidence that some genes are truly expressed and confer novel functions on the recipient insects. These include previously unavailable metabolic properties including digesting food, degrading toxins, providing resistance to pathogens, and facilitating an obligate mutualistic relationship with intracellular bacteria. A recent analysis revealed that an aphid gene of bacterial origin encodes a protein that is transported into the obligate symbiont, paralleling the evolution of endosymbiotic organelles. | 2015 | 32131363 |
| 747 | 3 | 0.9969 | S51 Family Peptidases Provide Resistance to Peptidyl-Nucleotide Antibiotic McC. Microcin C (McC)-like compounds are natural Trojan horse peptide-nucleotide antibiotics produced by diverse bacteria. The ribosomally synthesized peptide parts of these antibiotics are responsible for their facilitated transport into susceptible cells. Once inside the cell, the peptide part is degraded, releasing the toxic payload, an isoaspartyl-nucleotide that inhibits aspartyl-tRNA synthetase, an enzyme essential for protein synthesis. Bacteria that produce microcin C-like compounds have evolved multiple ways to avoid self-intoxication. Here, we describe a new strategy through the action of S51 family peptidases, which we name MccG. MccG cleaves the toxic isoaspartyl-nucleotide, rendering it inactive. While some MccG homologs are encoded by gene clusters responsible for biosynthesis of McC-like compounds, most are encoded by standalone genes whose products may provide a basal level of resistance to peptide-nucleotide antibiotics in phylogenetically distant bacteria. IMPORTANCE Here, we identified a natural substrate for a major phylogenetic clade of poorly characterized S51 family proteases from bacteria. We show that these proteins can contribute to a basal level of resistance to an important class of natural antibiotics. | 2022 | 35467414 |
| 9826 | 4 | 0.9968 | Horizontal genetic exchange, evolution, and spread of antibiotic resistance in bacteria. Some transformable bacteria have acquired target-mediated antibiotic resistance by horizontal genetic exchange of fragments of chromosomal genes. The resistant strains express variants of the antibiotic target that are metabolically active but exhibit a lowered affinity for the antibiotic. The alleles encoding these resistant proteins are mosaics comprising DNA derived from the host and other bacteria, often members of a different species. Examples include penicillin-resistant penicillin-binding proteins (PBPs) in Streptococcus pneumoniae and the pathogenic Neisseria species and sulfonamide-resistant dihydropterate synthase in Neisseria meningitidis. Distinct mosaic alleles encoding antibiotic resistance have arisen on multiple occasions, indicating the mobility of chromosomal genes in these species. Mosaic genes can arise at any chromosomal locus, and S. pneumoniae organisms with high-level penicillin resistance have acquired mosaic PBP genes at three bacterial bpb loci. Furthermore, horizontal genetic exchange permits movement of alleles among bacterial lineages, increasing the opportunities for the spread of antibiotic resistance. | 1998 | 9710667 |
| 190 | 5 | 0.9968 | The Two TpsB-Like Proteins in Anabaena sp. Strain PCC 7120 Are Involved in Secretion of Selected Substrates. The outer membrane of Gram-negative bacteria acts as an initial diffusion barrier that shields the cell from the environment. It contains many membrane-embedded proteins required for functionality of this system. These proteins serve as solute and lipid transporters or as machines for membrane insertion or secretion of proteins. The genome of Anabaena sp. strain PCC 7120 codes for two outer membrane transporters termed TpsB1 and TpsB2. They belong to the family of the two-partner secretion system proteins which are characteristic of pathogenic bacteria. Because pathogenicity of Anabaena sp. strain PCC 7120 has not been reported, the function of these two cyanobacterial TpsB proteins was analyzed. TpsB1 is encoded by alr1659, while TpsB2 is encoded by all5116 The latter is part of a genomic region containing 11 genes encoding TpsA-like proteins. However, tpsB2 is transcribed independently of a tpsA gene cluster. Bioinformatics analysis revealed the presence of at least 22 genes in Anabaena sp. strain PCC 7120 putatively coding for substrates of the TpsB system, suggesting a rather global function of the two TpsB proteins. Insertion of a plasmid into each of the two genes resulted in altered outer membrane integrity and antibiotic resistance. In addition, the expression of genes coding for the Clp and Deg proteases is dysregulated in these mutants. Moreover, for two of the putative substrates, a dependence of the secretion on functional TpsB proteins could be confirmed. We confirm the existence of a two-partner secretion system in Anabaena sp. strain PCC 7120 and predict a large pool of putative substrates.IMPORTANCE Cyanobacteria are important organisms for the ecosystem, considering their contribution to carbon fixation and oxygen production, while at the same time some species produce compounds that are toxic to their environment. As a consequence, cyanobacterial overpopulation might negatively impact the diversity of natural communities. Thus, a detailed understanding of cyanobacterial interaction with the environment, including other organisms, is required to define their impact on ecosystems. While two-partner secretion systems in pathogenic bacteria are well known, we provide a first description of the cyanobacterial two-partner secretion system. | 2021 | 33257527 |
| 9343 | 6 | 0.9968 | Origin of the bacterial SET domain genes: vertical or horizontal? The presence of Supressor of variegation-Enhanser of zeste-Trithorax (SET) domain genes in bacteria is a current paradigm for lateral genetic exchange between eukaryotes and prokaryotes. Because a major function of SET domain proteins is the chemical modification of chromatin and bacteria do not have chromatin, there is no apparent functional requirement for the existence of bacterial SET domain genes. Consequently, their finding in only a small fraction of pathogenic and symbiotic bacteria was taken as evidence that bacteria have obtained the SET domain genes from their hosts. Furthermore, it was proposed that the products of the genes would, most likely, be involved in bacteria-host interactions. The broadened scope of sequenced bacterial genomes to include also free-living and environmental species provided a larger sample to analyze the bacterial SET domain genes. By phylogenetic analysis, examination of individual chromosomal regions for signs of insertion, and evaluating the chromosomal versus SET domain genes' GC contents, we provide evidence that SET domain genes have existed in the bacterial domain of life independently of eukaryotes. The bacterial genes have undergone an evolution of their own unconnected to the evolution of the eukaryotic SET domain genes. Initial finding of SET domain genes in predominantly pathogenic and symbiotic bacteria resulted, most probably, from a biased sample. However, a lateral transfer of SET domain genes may have occurred between some bacteria and a family of Archaea. A model for the evolution and distribution of SET domain genes in bacteria is proposed. | 2007 | 17148507 |
| 765 | 7 | 0.9968 | Yeast ATP-binding cassette transporters: cellular cleaning pumps. Numerous ATP-binding cassette (ABC) proteins have been implicated in multidrug resistance, and some are also intimately connected to genetic diseases. For example, mammalian ABC proteins such as P-glycoproteins or multidrug resistance-associated proteins are associated with multidrug resistance phenomena (MDR), thus hampering anticancer therapy. Likewise, homologues in bacteria, fungi, or parasites are tightly associated with multidrug and antibiotic resistance. Several orthologues of mammalian MDR genes operate in the unicellular eukaryote Saccharomyces cerevisiae. Their functions have been linked to stress response, cellular detoxification, and drug resistance. This chapter discusses those yeast ABC transporters implicated in pleiotropic drug resistance and cellular detoxification. We describe strategies for their overexpression, biochemical purification, functional analysis, and a reconstitution in phospholipid vesicles, all of which are instrumental to better understanding their mechanisms of action and perhaps their physiological function. | 2005 | 16399365 |
| 8367 | 8 | 0.9968 | A hybrid NRPS-PKS gene cluster related to the bleomycin family of antitumor antibiotics in Alteromonas macleodii strains. Although numerous marine bacteria are known to produce antibiotics via hybrid NRPS-PKS gene clusters, none have been previously described in an Alteromonas species. In this study, we describe in detail a novel hybrid NRPS-PKS cluster identified in the plasmid of the Alteromonasmacleodii strain AltDE1 and analyze its relatedness to other similar gene clusters in a sequence-based characterization. This is a mobile cluster, flanked by transposase-like genes, that has even been found inserted into the chromosome of some Alteromonasmacleodii strains. The cluster contains separate genes for NRPS and PKS activity. The sole PKS gene appears to carry a novel acyltransferase domain, quite divergent from those currently characterized. The predicted specificities of the adenylation domains of the NRPS genes suggest that the final compound has a backbone very similar to bleomycin related compounds. However, the lack of genes involved in sugar biosynthesis indicates that the final product is not a glycopeptide. Even in the absence of these genes, the presence of the cluster appears to confer complete or partial resistance to phleomycin, which may be attributed to a bleomycin-resistance-like protein identified within the cluster. This also suggests that the compound still shares significant structural similarity to bleomycin. Moreover, transcriptomic evidence indicates that the NRPS-PKS cluster is expressed. Such sequence-based approaches will be crucial to fully explore and analyze the diversity and potential of secondary metabolite production, especially from increasingly important sources like marine microbes. | 2013 | 24069455 |
| 9346 | 9 | 0.9968 | Horizontal gene transfer in prokaryotes: quantification and classification. Comparative analysis of bacterial, archaeal, and eukaryotic genomes indicates that a significant fraction of the genes in the prokaryotic genomes have been subject to horizontal transfer. In some cases, the amount and source of horizontal gene transfer can be linked to an organism's lifestyle. For example, bacterial hyperthermophiles seem to have exchanged genes with archaea to a greater extent than other bacteria, whereas transfer of certain classes of eukaryotic genes is most common in parasitic and symbiotic bacteria. Horizontal transfer events can be classified into distinct categories of acquisition of new genes, acquisition of paralogs of existing genes, and xenologous gene displacement whereby a gene is displaced by a horizontally transferred ortholog from another lineage (xenolog). Each of these types of horizontal gene transfer is common among prokaryotes, but their relative contributions differ in different lineages. The fixation and long-term persistence of horizontally transferred genes suggests that they confer a selective advantage on the recipient organism. In most cases, the nature of this advantage remains unclear, but detailed examination of several cases of acquisition of eukaryotic genes by bacteria seems to reveal the evolutionary forces involved. Examples include isoleucyl-tRNA synthetases whose acquisition from eukaryotes by several bacteria is linked to antibiotic resistance, ATP/ADP translocases acquired by intracellular parasitic bacteria, Chlamydia and Rickettsia, apparently from plants, and proteases that may be implicated in chlamydial pathogenesis. | 2001 | 11544372 |
| 764 | 10 | 0.9967 | Fungal ATP-binding cassette (ABC) transporters in drug resistance & detoxification. Pleiotropic drug resistance (PDR) is a well-described phenomenon occurring in fungi. PDR shares several similarities with processes in bacteria and higher eukaryotes. In mammalian cells, multidrug resistance (MDR) develops from an initial single drug resistance, eventually leading to a broad cross-resistance to many structurally and functionally unrelated compounds. Notably, a number of membrane-embedded energy-consuming ATP-binding cassette (ABC) transporters have been implicated in the development of PDR/MDR phenotypes. The yeast Saccharomyces cerevisiae genome harbors some 30 genes encoding ABC proteins, several of which mediate PDR. Therefore, yeast served as an important model organism to study the functions of evolutionary conserved ABC genes, including those mediating clinical antifungal resistance in fungal pathogens. Moreover, yeast cells lacking endogenous ABC pumps are hypersensitive to many antifungal drugs, making them suitable for functional studies and cloning of ABC transporters from fungal pathogens such as Candida albicans. This review discusses drug resistance phenomena mediated by ABC transporters in the model system S. cerevisiae and certain fungal pathogens. | 2006 | 16611035 |
| 9344 | 11 | 0.9967 | A comparative study indicates vertical inheritance and horizontal gene transfer of arsenic resistance-related genes in eukaryotes. Arsenic is a ubiquitous element in the environment, a source of constant evolutionary pressure on organisms. The arsenic resistance machinery is thoroughly described for bacteria. Highly resistant lineages are also common in eukaryotes, but evolutionary knowledge is much more limited. While the origin of the resistance machinery in eukaryotes is loosely attributed to horizontal gene transfer (HGT) from bacteria, only a handful of eukaryotes were deeply studied. Here we investigate the origin and evolution of the core genes in arsenic resistance in eukaryotes using a broad phylogenetic framework. We hypothesize that, as arsenic pressure is constant throughout Earth's history, resistance mechanisms are probably ancestral to eukaryotes. We identified homologs for each of the arsenic resistance genes in eukaryotes and traced their possible origin using phylogenetic reconstruction. We reveal that: i. an important component of the arsenic-resistant machinery originated before the last eukaryotic common ancestor; ii. later events of gene duplication and HGT generated new homologs that, in many cases, replaced ancestral ones. Even though HGT has an important contribution to the expansion of arsenic metabolism in eukaryotes, we propose the hypothesis of ancestral origin and differential retention of arsenic resistance mechanisms in the group. Key-words: Environmental adaptation; resistance to toxic metalloids; detoxification; comparative genomics; functional phylogenomics. | 2022 | 35533945 |
| 9987 | 12 | 0.9967 | Four genes essential for recombination define GInts, a new type of mobile genomic island widespread in bacteria. Integrases are a family of tyrosine recombinases that are highly abundant in bacterial genomes, actively disseminating adaptive characters such as pathogenicity determinants and antibiotics resistance. Using comparative genomics and functional assays, we identified a novel type of mobile genetic element, the GInt, in many diverse bacterial groups but not in archaea. Integrated as genomic islands, GInts show a tripartite structure consisting of the ginABCD operon, a cargo DNA region from 2.5 to at least 70 kb, and a short AT-rich 3' end. The gin operon is characteristic of GInts and codes for three putative integrases and a small putative helix-loop-helix protein, all of which are essential for integration and excision of the element. Genes in the cargo DNA are acquired mostly from phylogenetically related bacteria and often code for traits that might increase fitness, such as resistance to antimicrobials or virulence. GInts also tend to capture clusters of genes involved in complex processes, such as the biosynthesis of phaseolotoxin by Pseudomonas syringae. GInts integrate site-specifically, generating two flanking direct imperfect repeats, and excise forming circular molecules. The excision process generates sequence variants at the element attachment site, which can increase frequency of integration and drive target specificity. | 2017 | 28393892 |
| 167 | 13 | 0.9967 | Ion efflux systems involved in bacterial metal resistances. Studying metal ion resistance gives us important insights into environmental processes and provides an understanding of basic living processes. This review concentrates on bacterial efflux systems for inorganic metal cations and anions, which have generally been found as resistance systems from bacteria isolated from metal-polluted environments. The protein products of the genes involved are sometimes prototypes of new families of proteins or of important new branches of known families. Sometimes, a group of related proteins (and presumedly the underlying physiological function) has still to be defined. For example, the efflux of the inorganic metal anion arsenite is mediated by a membrane protein which functions alone in Gram-positive bacteria, but which requires an additional ATPase subunit in some Gram-negative bacteria. Resistance to Cd2+ and Zn2+ in Gram-positive bacteria is the result of a P-type efflux ATPase which is related to the copper transport P-type ATPases of bacteria and humans (defective in the human hereditary diseases Menkes' syndrome and Wilson's disease). In contrast, resistance to Zn2+, Ni2+, Co2+ and Cd2+ in Gram-negative bacteria is based on the action of proton-cation antiporters, members of a newly-recognized protein family that has been implicated in diverse functions such as metal resistance/nodulation of legumes/cell division (therefore, the family is called RND). Another new protein family, named CDF for 'cation diffusion facilitator' has as prototype the protein CzcD, which is a regulatory component of a cobalt-zinc-cadmium resistance determinant in the Gram-negative bacterium Alcaligenes eutrophus. A family for the ChrA chromate resistance system in Gram-negative bacteria has still to be defined. | 1995 | 7766211 |
| 284 | 14 | 0.9967 | Expression of a transposable antibiotic resistance element in Saccharomyces. Some eukaryotic genes can be expressed in bacteria but there are few examples of the expression of prokaryotic genes in eukaryotes. Antibiotic G418 is a 2-deoxystreptamine antibiotic that is structurally related to gentamicin but has inhibitory activity against a much wider variety of pro- and eukaryotic organisms. In bacteria, resistance to G418 can be determined by several plasmid-encoded modifiying enzymes and, in view of the broad spectrum of activity of G418, we considered that this antibiotic might be useful as a selective agent for the introduction of these antibiotic resistance genes into a eukaryotic organism such as Saccharomyces cerevisiae. Additional impetus for these experiments came from the knowledge that certain of the G418-resistance determinants in bacteria are carried on transposable elements; a study of the properties of these elements in eukaryotes would be intriguing. | 1980 | 6253817 |
| 177 | 15 | 0.9967 | Bacterial mercury resistance from atoms to ecosystems. Bacterial resistance to inorganic and organic mercury compounds (HgR) is one of the most widely observed phenotypes in eubacteria. Loci conferring HgR in Gram-positive or Gram-negative bacteria typically have at minimum a mercuric reductase enzyme (MerA) that reduces reactive ionic Hg(II) to volatile, relatively inert, monoatomic Hg(0) vapor and a membrane-bound protein (MerT) for uptake of Hg(II) arranged in an operon under control of MerR, a novel metal-responsive regulator. Many HgR loci encode an additional enzyme, MerB, that degrades organomercurials by protonolysis, and one or more additional proteins apparently involved in transport. Genes conferring HgR occur on chromosomes, plasmids, and transposons and their operon arrangements can be quite diverse, frequently involving duplications of the above noted structural genes, several of which are modular themselves. How this very mobile and plastic suite of proteins protects host cells from this pervasive toxic metal, what roles it has in the biogeochemical cycling of Hg, and how it has been employed in ameliorating environmental contamination are the subjects of this review. | 2003 | 12829275 |
| 9846 | 16 | 0.9967 | Integrative Conjugative Elements (ICEs) of the SXT/R391 family drive adaptation and evolution in γ-Proteobacteria. Integrative Conjugative Elements (ICEs) are mosaics containing functional modules allowing maintenance by site-specific integration and excision into and from the host genome and conjugative transfer to a specific host range. Many ICEs encode a range of adaptive functions that aid bacterial survival and evolution in a range of niches. ICEs from the SXT/R391 family are found in γ-Proteobacteria. Over 100 members have undergone epidemiological and molecular characterization allowing insight into their diversity and function. Comparative analysis of SXT/R391 elements from a wide geographic distribution has revealed conservation of key functions, and the accumulation and evolution of adaptive genes. This evolution is associated with gene acquisition in conserved hotspots and variable regions within the SXT/R391 ICEs catalysed via element-encoded recombinases. The elements can carry IS elements and transposons, and a mutagenic DNA polymerase, PolV, which are associated with their evolution. SXT/R391 ICEs isolated from different niches appear to have retained adaptive functions related to that specific niche; phage resistance determinants in ICEs carried by wastewater bacteria, antibiotic resistance determinants in clinical isolates and metal resistance determinants in bacteria recovered from polluted environments/ocean sediments. Many genes found in the element hotspots are undetermined and have few homologs in the nucleotide databases. | 2024 | 36634159 |
| 9986 | 17 | 0.9967 | Identification and characterization of thousands of bacteriophage satellites across bacteria. Bacteriophage-bacteria interactions are affected by phage satellites, elements that exploit phages for transfer between bacteria. Satellites can encode defense systems, antibiotic resistance genes, and virulence factors, but their number and diversity are unknown. We developed SatelliteFinder to identify satellites in bacterial genomes, detecting the four best described families: P4-like, phage inducible chromosomal islands (PICI), capsid-forming PICI, and PICI-like elements (PLE). We vastly expanded the number of described elements to ∼5000, finding bacterial genomes with up to three different families of satellites. Most satellites were found in Proteobacteria and Firmicutes, but some are in novel taxa such as Actinobacteria. We characterized the gene repertoires of satellites, which are variable in size and composition, and their genomic organization, which is very conserved. Phylogenies of core genes in PICI and cfPICI indicate independent evolution of their hijacking modules. There are few other homologous core genes between other families of satellites, and even fewer homologous to phages. Hence, phage satellites are ancient, diverse, and probably evolved multiple times independently. Given the many bacteria infected by phages that still lack known satellites, and the recent proposals for novel families, we speculate that we are at the beginning of the discovery of massive numbers and types of satellites. | 2023 | 36869669 |
| 564 | 18 | 0.9967 | Mycobacterium tuberculosis possesses an unusual tmRNA rescue system. Trans-translation is a key process in bacteria which recycles stalled ribosomes and tags incomplete nascent proteins for degradation. This ensures the availability of ribosomes for protein synthesis and prevents the accumulation of dysfunctional proteins. The tmRNA, ssrA, is responsible for both recovering stalled ribosomes and encodes the degradation tag; ssrA associates and functions with accessory proteins such as SmpB. Although ssrA and smpB are ubiquitous in bacteria, they are not essential for the viability of many species. The Mycobacterium tuberculosis genome has homologues of both ssrA and smpB. We demonstrated that ssrA is essential in M. tuberculosis, since the chromosomal copy of the gene could only be deleted in the presence of a functional copy integrated elsewhere. However, we were able to delete the proteolytic tagging function by constructing strains carrying a mutant allele (ssrADD). This demonstrates that ribosome rescue by ssrA is the essential function in M. tuberculosis, SmpB was not required for aerobic growth, since we were able to construct a deletion strain. However, the smpBΔ strain was more sensitive to antibiotics targeting the ribosome. Strains with deletion of smpB or mutations in ssrA did not show increased sensitivity (or resistance) to pyrazinamide suggesting that this antibiotic does not directly target these components of the tmRNA tagging system. | 2014 | 24145139 |
| 179 | 19 | 0.9967 | The genetics and biochemistry of mercury resistance. The ability of bacteria to detoxify mercurial compounds by reduction and volatilization is conferred by mer genes, which are usually plasmid located. The narrow spectrum (Hg2+ detoxifying) Tn501 and R100 determinants have been subjected to molecular genetic and DNA sequence analysis. Biochemical studies on the flavoprotein mercuric reductase have elucidated the mechanism of reduction of Hg2+ to Hg0. The mer genes have been mapped and sequenced and their protein products studied in minicells. Based on the deduced amino acid sequences, these proteins have been assigned a role in a mechanistic scheme for mercury flux in resistant bacteria. The mer genes are inducible, with regulatory control being exerted at the transcriptional level both positively and negatively. Attention is now focusing on broad-spectrum resistance involving detoxification of organomercurials by an additional enzyme, organomercurial lyase. Lyase genes have recently been cloned and sequencing studies are in progress. | 1987 | 2827958 |