# | Rank | Similarity | Title + Abs. | Year | PMID |
|---|---|---|---|---|---|
| 0 | 1 | 2 | 3 | 4 | 5 |
| 8421 | 0 | 0.9897 | Dynamic stepwise opening of integron attC DNA hairpins by SSB prevents toxicity and ensures functionality. Biologically functional DNA hairpins are found in archaea, prokaryotes and eukaryotes, playing essential roles in various DNA transactions. However, during DNA replication, hairpin formation can stall the polymerase and is therefore prevented by the single-stranded DNA binding protein (SSB). Here, we address the question how hairpins maintain their functional secondary structure despite SSB's presence. As a model hairpin, we used the recombinogenic form of the attC site, essential for capturing antibiotic-resistance genes in the integrons of bacteria. We found that attC hairpins have a conserved high GC-content near their apical loop that creates a dynamic equilibrium between attC fully opened by SSB and a partially structured attC-6-SSB complex. This complex is recognized by the recombinase IntI, which extrudes the hairpin upon binding while displacing SSB. We anticipate that this intriguing regulation mechanism using a base pair distribution to balance hairpin structure formation and genetic stability is key to the dissemination of antibiotic resistance genes among bacteria and might be conserved among other functional hairpins. | 2017 | 28985409 |
| 9834 | 1 | 0.9895 | Exploring the role of phage plasmids in gene transfers. Bacteriophages and plasmids drive horizontal gene transfer (HGT) in bacteria. Phage-plasmids (P-Ps) are hybrids of plasmid and phages. Pfeifer and Rocha recently demonstrated that P-Ps can serve as intermediates in gene exchanges between these two types of elements, identified categories of preferentially transferred genes, and reconstructed gene flows involving phage P1-like P-Ps. | 2024 | 38688811 |
| 9817 | 2 | 0.9895 | Common regions e.g. orf513 and antibiotic resistance: IS91-like elements evolving complex class 1 integrons. The ability of bacteria to procure, sometimes rearrange, and evince acquired DNA continues to impress us-even more so if this genetic plasticity involves the sequestering of antibiotic resistance genes. The acquisition of genes in bacteria is often facilitated by transposons, integrons and archetype insertion elements. Recently however, a new element, 'orf513', has been increasingly associated with class 1 integrons. Moreover, these 'complex' class 1 integrons can potentially mediate resistance to chloramphenicol, trimethoprim, aminoglycosides and tetracycline and may carry a range of beta-lactamase genes as well as the qnrA gene. Elements such as 'orf513' demonstrate IS91-like characteristics and will mobilize adjacent DNA via a process called rolling circle replication, and thus we have renamed them 'insertion sequence CRs' (ISCRs) to appropriately reflect their structure-function properties. In this article, we provide a brief description of these new and clinically important mobile elements, and how they are able to mobilize antibiotic resistance genes. | 2006 | 16751201 |
| 9084 | 3 | 0.9894 | Disrupting antibiotic resistance propagation by inhibiting the conjugative DNA relaxase. Conjugative transfer of plasmid DNA via close cell-cell junctions is the main route by which antibiotic resistance genes spread between bacterial strains. Relaxases are essential for conjugative transfer and act by cleaving DNA strands and forming covalent phosphotyrosine linkages. Based on data indicating that multityrosine relaxase enzymes can accommodate two phosphotyrosine intermediates within their divalent metal-containing active sites, we hypothesized that bisphosphonates would inhibit relaxase activity and conjugative DNA transfer. We identified bisphosphonates that are nanomolar inhibitors of the F plasmid conjugative relaxase in vitro. Furthermore, we used cell-based assays to demonstrate that these compounds are highly effective at preventing DNA transfer and at selectively killing cells harboring conjugative plasmids. Two potent inhibitors, clodronate and etidronate, are already clinically approved to treat bone loss. Thus, the inhibition of conjugative relaxases is a potentially novel antimicrobial approach, one that selectively targets bacteria capable of transferring antibiotic resistance and generating multidrug resistant strains. | 2007 | 17630285 |
| 3001 | 4 | 0.9894 | IS26 and the IS26 family: versatile resistance gene movers and genome reorganizers. SUMMARYIn Gram-negative bacteria, the insertion sequence IS26 is highly active in disseminating antibiotic resistance genes. IS26 can recruit a gene or group of genes into the mobile gene pool and support their continued dissemination to new locations by creating pseudo-compound transposons (PCTs) that can be further mobilized by the insertion sequence (IS). IS26 can also enhance expression of adjacent potential resistance genes. IS26 encodes a DDE transposase but has unique properties. It forms cointegrates between two separate DNA molecules using two mechanisms. The well-known copy-in (replicative) route generates an additional IS copy and duplicates the target site. The recently discovered and more efficient and targeted conservative mechanism requires an IS in both participating molecules and does not generate any new sequence. The unit of movement for PCTs, known as a translocatable unit or TU, includes only one IS26. TU formed by homologous recombination between the bounding IS26s can be reincorporated via either cointegration route. However, the targeted conservative reaction is key to generation of arrays of overlapping PCTs seen in resistant pathogens. Using the copy-in route, IS26 can also act on a site in the same DNA molecule, either inverting adjacent DNA or generating an adjacent deletion plus a circular molecule carrying the DNA segment lost and an IS copy. If reincorporated, these circular molecules create a new PCT. IS26 is the best characterized IS in the IS26 family, which includes IS257/IS431, ISSau10, IS1216, IS1006, and IS1008 that are also implicated in spreading resistance genes in Gram-positive and Gram-negative pathogens. | 2024 | 38436262 |
| 9832 | 5 | 0.9894 | Interplay between the Xer recombination system and the dissemination of antibioresistance in Acinetobacter baumannii. Antibiotic-resistant infections are a pressing clinical challenge. Plasmids are known to accelerate the emergence of resistance by facilitating horizontal gene transfer of antibiotic resistance genes between bacteria. We explore this question in Acinetobacter baumannii, a globally emerging nosocomial pathogen responsible for a wide range of infections with a worrying accumulation of resistance, particularly involving plasmids. In this species, plasmids of the Rep_3 family harbor antibiotic resistance genes within variable regions flanked by potential site-specific recombination sites recognized by the XerCD recombinase. We first show that the Xer system of A. baumannii functions as described in Escherichia coli, resolving chromosome dimers at the dif site and recombining plasmid-carried sites. However, the multiple Xer recombination sites found in Rep_3 plasmids do not allow excision of plasmid fragments. Rather, they recombine to cointegrate plasmids, which could then evolve to exchange genes. Cointegrates represent a significant fraction of the plasmid population and their formation is controlled by the sequence of recombination sites, which determines the compatibility between recombination sites. We conclude that plasmids in A. baumannii frequently recombine by Xer recombination, allowing a high level of yet controlled plasticity in the acquisition and combination of antibiotic resistance genes. | 2025 | 39777461 |
| 9843 | 6 | 0.9894 | Conjugative transposons: an unusual and diverse set of integrated gene transfer elements. Conjugative transposons are integrated DNA elements that excise themselves to form a covalently closed circular intermediate. This circular intermediate can either reintegrate in the same cell (intracellular transposition) or transfer by conjugation to a recipient and integrate into the recipient's genome (intercellular transposition). Conjugative transposons were first found in gram-positive cocci but are now known to be present in a variety of gram-positive and gram-negative bacteria also. Conjugative transposons have a surprisingly broad host range, and they probably contribute as much as plasmids to the spread of antibiotic resistance genes in some genera of disease-causing bacteria. Resistance genes need not be carried on the conjugative transposon to be transferred. Many conjugative transposons can mobilize coresident plasmids, and the Bacteroides conjugative transposons can even excise and mobilize unlinked integrated elements. The Bacteroides conjugative transposons are also unusual in that their transfer activities are regulated by tetracycline via a complex regulatory network. | 1995 | 8531886 |
| 2999 | 7 | 0.9894 | Integrative and conjugative elements in streptococci can act as vectors for plasmids and translocatable units integrated via IS1216E. Mobile genetic elements (MGEs), such as integrative and conjugative elements (ICEs), plasmids and translocatable units (TUs), are important drivers for the spread of antibiotic resistance. Although ICEs have been reported to support the spread of plasmids among different bacteria, their role in mobilizing resistance plasmids and TUs has not yet been fully explored. In this study, a novel TU bearing optrA, a novel non-conjugative plasmid p5303-cfrD carrying cfr(D) and a new member of the ICESa2603 family, ICESg5301 were identified in streptococci. Polymerase chain reaction (PCR) assays revealed that three different types of cointegrates can be formed by IS1216E-mediated cointegration between the three different MGEs, including ICESg5301::p5303-cfrD::TU, ICESg5301::p5303-cfrD, and ICESg5301::TU. Conjugation assays showed that ICEs carrying p5303-cfrD and/or TU successfully transferred into recipient strains, thereby confirming that ICEs can serve as vectors for other non-conjugative MGEs, such as TUs and p5303-cfrD. As neither the TU nor plasmid p5303-cfrD can spread on their own between different bacteria, their integration into an ICE via IS1216E-mediated cointegrate formation not only increases the plasticity of ICEs, but also furthers the dissemination of plasmids and TUs carrying oxazolidinone resistance genes. | 2023 | 36933870 |
| 9853 | 8 | 0.9893 | The master activator of IncA/C conjugative plasmids stimulates genomic islands and multidrug resistance dissemination. Dissemination of antibiotic resistance genes occurs mostly by conjugation, which mediates DNA transfer between cells in direct contact. Conjugative plasmids of the IncA/C incompatibility group have become a substantial threat due to their broad host-range, the extended spectrum of antimicrobial resistance they confer, their prevalence in enteric bacteria and their very efficient spread by conjugation. However, their biology remains largely unexplored. Using the IncA/C conjugative plasmid pVCR94ΔX as a prototype, we have investigated the regulatory circuitry that governs IncA/C plasmids dissemination and found that the transcriptional activator complex AcaCD is essential for the expression of plasmid transfer genes. Using chromatin immunoprecipitation coupled with exonuclease digestion (ChIP-exo) and RNA sequencing (RNA-seq) approaches, we have identified the sequences recognized by AcaCD and characterized the AcaCD regulon. Data mining using the DNA motif recognized by AcaCD revealed potential AcaCD-binding sites upstream of genes involved in the intracellular mobility functions (recombination directionality factor and mobilization genes) in two widespread classes of genomic islands (GIs) phylogenetically unrelated to IncA/C plasmids. The first class, SGI1, confers and propagates multidrug resistance in Salmonella enterica and Proteus mirabilis, whereas MGIVmi1 in Vibrio mimicus belongs to a previously uncharacterized class of GIs. We have demonstrated that through expression of AcaCD, IncA/C plasmids specifically trigger the excision and mobilization of the GIs at high frequencies. This study provides new evidence of the considerable impact of IncA/C plasmids on bacterial genome plasticity through their own mobility and the mobilization of genomic islands. | 2014 | 25340549 |
| 9851 | 9 | 0.9893 | The potential of integrons and connected programmed rearrangements for mediating horizontal gene transfer. Site-specific recombination of integrons, mediates transfer of single genes in small genomes and plasmids. Recent data suggest that new genes are recruited to the cassettes--the units moved by integrons. Integrons are resident in a class of transposons with pronounced target selectivity for resolution loci in broad host range plasmids. A resulting network of programmed transfer routes, with potential offshoots reaching into eukaryotic cells, may channel genes to unexpectedly remote organisms. It has previously been observed that the conjugation apparatus of the broad host range plasmid R751 (IncP) which contains transposon Tn5090 harbouring an integron, promotes horizontal genetic transfer between bacteria and yeast. Furthermore, it is well known and fundamental for widely used gene replacement technologies, that site-specific recombination systems (e.g. Cre-lox of bacteriophage P1) related to the integrons are functional in higher eukaryotes. It seems very clear that integrons and associated programmed transfer mechanisms have high significance for the dissemination of antibiotic resistance genes in bacteria whereas further studies are needed to assess their importance for spreading of arbitrary genes in a wider range of host systems. | 1998 | 9850680 |
| 9831 | 10 | 0.9893 | An antiplasmid system drives antibiotic resistance gene integration in carbapenemase-producing Escherichia coli lineages. Plasmids carrying antibiotic resistance genes (ARG) are the main mechanism of resistance dissemination in Enterobacterales. However, the fitness-resistance trade-off may result in their elimination. Chromosomal integration of ARGs preserves resistance advantage while relieving the selective pressure for keeping costly plasmids. In some bacterial lineages, such as carbapenemase producing sequence type ST38 Escherichia coli, most ARGs are chromosomally integrated. Here we reproduce by experimental evolution the mobilisation of the carbapenemase bla(OXA-48) gene from the pOXA-48 plasmid into the chromosome. We demonstrate that this integration depends on a plasmid-induced fitness cost, a mobile genetic structure embedding the ARG and a novel antiplasmid system ApsAB actively involved in pOXA-48 destabilization. We show that ApsAB targets high and low-copy number plasmids. ApsAB combines a nuclease/helicase protein and a novel type of Argonaute-like protein. It belongs to a family of defense systems broadly distributed among bacteria, which might have a strong ecological impact on plasmid diffusion. | 2024 | 38750030 |
| 9818 | 11 | 0.9893 | ISCR elements: novel gene-capturing systems of the 21st century? "Common regions" (CRs), such as Orf513, are being increasingly linked to mega-antibiotic-resistant regions. While their overall nucleotide sequences show little identity to other mobile elements, amino acid alignments indicate that they possess the key motifs of IS91-like elements, which have been linked to the mobility ent plasmids in pathogenic Escherichia coli. Further inspection reveals that they possess an IS91-like origin of replication and termination sites (terIS), and therefore CRs probably transpose via a rolling-circle replication mechanism. Accordingly, in this review we have renamed CRs as ISCRs to give a more accurate reflection of their functional properties. The genetic context surrounding ISCRs indicates that they can procure 5' sequences via misreading of the cognate terIS, i.e., "unchecked transposition." Clinically, the most worrying aspect of ISCRs is that they are increasingly being linked with more potent examples of resistance, i.e., metallo-beta-lactamases in Pseudomonas aeruginosa and co-trimoxazole resistance in Stenotrophomonas maltophilia. Furthermore, if ISCR elements do move via "unchecked RC transposition," as has been speculated for ISCR1, then this mechanism provides antibiotic resistance genes with a highly mobile genetic vehicle that could greatly exceed the effects of previously reported mobile genetic mechanisms. It has been hypothesized that bacteria will surprise us by extending their "genetic construction kit" to procure and evince additional DNA and, therefore, antibiotic resistance genes. It appears that ISCR elements have now firmly established themselves within that regimen. | 2006 | 16760305 |
| 9833 | 12 | 0.9892 | Evolution of satellite plasmids can prolong the maintenance of newly acquired accessory genes in bacteria. Transmissible plasmids spread genes encoding antibiotic resistance and other traits to new bacterial species. Here we report that laboratory populations of Escherichia coli with a newly acquired IncQ plasmid often evolve 'satellite plasmids' with deletions of accessory genes and genes required for plasmid replication. Satellite plasmids are molecular parasites: their presence reduces the copy number of the full-length plasmid on which they rely for their continued replication. Cells with satellite plasmids gain an immediate fitness advantage from reducing burdensome expression of accessory genes. Yet, they maintain copies of these genes and the complete plasmid, which potentially enables them to benefit from and transmit the traits they encode in the future. Evolution of satellite plasmids is transient. Cells that entirely lose accessory gene function or plasmid mobility dominate in the long run. Satellite plasmids also evolve in Snodgrassella alvi colonizing the honey bee gut, suggesting that this mechanism may broadly contribute to the importance of IncQ plasmids as agents of bacterial gene transfer in nature. | 2019 | 31863068 |
| 9960 | 13 | 0.9892 | Integrons, transposons and IS elements promote diversification of multidrug resistance plasmids and adaptation of their hosts to antibiotic pollutants from pharmaceutical companies. Plasmids are important vehicles for the dissemination of antibiotic resistance genes (ARGs) among bacteria by conjugation. Here, we determined the complete nucleotide sequences of nine different plasmids previously obtained by exogenous plasmid isolation from river and creek sediments and wastewater from a pharmaceutical company. We identified six IncP/P-1ε plasmids and single members of IncL, IncN and IncFII-like plasmids. Genetic structures of the accessory regions of the IncP/P-1ε plasmids obtained implied that multiple insertions and deletions had occurred, mediated by different transposons and Class 1 integrons with various ARGs. Our study provides compelling evidence that Class 1 integrons, Tn402-like transposons, Tn3-like transposons and/or IS26 played important roles in the acquisition of ARGs across all investigated plasmids. Our plasmid sequencing data provide new insights into how these mobile genetic elements could mediate the acquisition and spread of ARGs in environmental bacteria. | 2023 | 37655671 |
| 348 | 14 | 0.9892 | Conjugative DNA transfer in Streptomyces by TraB: is one protein enough? Antibiotic-producing soil bacteria of the genus Streptomyces form a huge natural reservoir of antibiotic resistance genes for the dissemination within the soil community. Streptomyces plasmids encode a unique conjugative DNA transfer system clearly distinguished from classical conjugation involving a single-stranded DNA molecule and a type IV protein secretion system. Only a single plasmid-encoded protein, TraB, is sufficient to translocate a double-stranded DNA molecule into the recipient in Streptomyces matings. TraB is a hexameric pore-forming ATPase that resembles the chromosome segregator protein FtsK and translocates DNA by recognizing specific 8-bp repeats present in the plasmid clt locus. Mobilization of chromosomal genes does not require integration of the plasmid, because TraB also recognizes clt-like sequences distributed all over the chromosome. | 2012 | 23082971 |
| 9848 | 15 | 0.9891 | Cargo Genes of Tn7-Like Transposons Comprise an Enormous Diversity of Defense Systems, Mobile Genetic Elements, and Antibiotic Resistance Genes. Transposition is a major mechanism of horizontal gene mobility in prokaryotes. However, exploration of the genes mobilized by transposons (cargo) is hampered by the difficulty in delineating integrated transposons from their surrounding genetic context. Here, we present a computational approach that allowed us to identify the boundaries of 6,549 Tn7-like transposons. We found that 96% of these transposons carry at least one cargo gene. Delineation of distinct communities in a gene-sharing network demonstrates how transposons function as a conduit of genes between phylogenetically distant hosts. Comparative analysis of the cargo genes reveals significant enrichment of mobile genetic elements (MGEs) nested within Tn7-like transposons, such as insertion sequences and toxin-antitoxin modules, and of genes involved in recombination, anti-MGE defense, and antibiotic resistance. More unexpectedly, cargo also includes genes encoding central carbon metabolism enzymes. Twenty-two Tn7-like transposons carry both an anti-MGE defense system and antibiotic resistance genes, illustrating how bacteria can overcome these combined pressures upon acquisition of a single transposon. This work substantially expands the distribution of Tn7-like transposons, defines their evolutionary relationships, and provides a large-scale functional classification of prokaryotic genes mobilized by transposition. IMPORTANCE Transposons are major vehicles of horizontal gene transfer that, in addition to genes directly involved in transposition, carry cargo genes. However, characterization of these genes is hampered by the difficulty of identification of transposon boundaries. We developed a computational approach for detecting transposon ends and applied it to perform a comprehensive census of the cargo genes of Tn7-like transposons, a large class of bacterial mobile genetic elements (MGE), many of which employ a unique, CRISPR-mediated mechanism of site-specific transposition. The cargo genes encompass a striking diversity of MGE, defense, and antibiotic resistance systems. Unexpectedly, we also identified cargo genes encoding metabolic enzymes. Thus, Tn7-like transposons mobilize a vast repertoire of genes that can have multiple effects on the host bacteria. | 2021 | 34872347 |
| 309 | 16 | 0.9891 | Evolution of a Plasmid Regulatory Circuit Ameliorates Plasmid Fitness Cost. Plasmids promote adaptation of bacteria by facilitating horizontal transfer of diverse genes, notably those conferring antibiotic resistance. Some plasmids, like those of the incompatibility group IncP-1, are known to replicate and persist in a broad range of bacteria. We investigated a poorly understood exception, the IncP-1β plasmid pBP136 from a clinical Bordetella pertussis isolate, which quickly became extinct in laboratory Escherichia coli populations. Through experimental evolution, we found that the inactivation of a previously uncharacterized plasmid gene, upf31, drastically improved plasmid persistence in E. coli. The gene inactivation caused alterations in the plasmid regulatory system, including decreased transcription of the global plasmid regulators (korA, korB, and korC) and numerous genes in their regulons. This is consistent with our findings that Upf31 represses its own transcription. It also caused secondary transcriptional changes in many chromosomal genes. In silico analyses predicted that Upf31 interacts with the plasmid regulator KorB at its C-terminal dimerization domain (CTD). We showed experimentally that adding the CTD of upf31/pBP136 to the naturally truncated upf31 allele of the stable IncP-1β archetype R751 results in plasmid destabilization in E. coli. Moreover, mutagenesis showed that upf31 alleles encoded on nearly half of the sequenced IncP-1β plasmids also possess this destabilization phenotype. While Upf31 might be beneficial in many hosts, we show that in E. coli some alleles have harmful effects that can be rapidly alleviated with a single mutation. Thus, broad-host-range plasmid adaptation to new hosts can involve fine-tuning their transcriptional circuitry through evolutionary changes in a single gene. | 2025 | 40138356 |
| 9854 | 17 | 0.9891 | Unraveling the regulatory network of IncA/C plasmid mobilization: When genomic islands hijack conjugative elements. Conjugative plasmids of the A/C incompatibility group (IncA/C) have become substantial players in the dissemination of multidrug resistance. These large conjugative plasmids are characterized by their broad host-range, extended spectrum of antimicrobials resistance, and prevalence in enteric bacteria recovered from both environmental and clinical settings. Until recently, relatively little was known about the basic biology of IncA/C plasmids, mostly because of the hindrance of multidrug resistance for molecular biology experiments. To circumvent this issue, we previously developed pVCR94ΔX, a convenient prototype that codes for a reduced set of antibiotic resistances. Using pVCR94ΔX, we then characterized the regulatory pathway governing IncA/C plasmid dissemination. We found that the expression of roughly 2 thirds of the genes encoded by this plasmid, including large operons involved in the conjugation process, depends on an FlhCD-like master activator called AcaCD. Beyond the mobility of IncA/C plasmids, AcaCD was also shown to play a key role in the mobilization of different classes of genomic islands (GIs) identified in various pathogenic bacteria. By doing so, IncA/C plasmids can have a considerable impact on bacterial genomes plasticity and evolution. | 2015 | 26442183 |
| 9246 | 18 | 0.9891 | Horizontal Gene Transfer Systems for Spread of Antibiotic Resistance in Gram-Negative Bacteria. Antibiotic-resistant bacteria have become a significant global threat to public health due to the increasing difficulty in treatment. These bacteria acquire resistance by incorporating various antibiotic resistance genes (ARGs) through specialized gene transfer mechanisms, allowing them to evade antibiotic attacks. Conjugation, transformation, and transduction are well-established mechanisms that drive the acquisition and dissemination of ARGs in Gram-negative bacteria. In particular, the horizontal transfer of plasmids carrying multiple ARGs is highly problematic, as it can instantly convert susceptible bacteria into multidrug-resistant ones. Transduction, mediated by bacteriophages that package ARG-containing chromosomal DNA from host cells, also plays a crucial role in ARG spread without requiring direct cell-to-cell contact. Recently, a novel horizontal gene transfer (HGT) mechanism involving outer membrane vesicles (OMVs) has been identified as a key player in ARG dissemination. OMVs-nanoscale, spherical structures produced by bacteria during growth-have been found to carry small plasmids and chromosomal DNA fragments containing ARGs from their host bacteria. This newly discovered transfer process, termed "vesiduction," enables intercellular DNA exchange and further contributes to the spread of antibiotic resistance. Additionally, mobile genetic elements such as transposons, insertion sequences, and site-specific recombination systems like integrons facilitate rearrangement of ARGs, including their translocation between chromosomes and plasmids. This review explores the molecular mechanisms underlying the HGT of ARGs, with a particular focus on clinically isolated antibiotic-resistant Gram-negative bacteria. | 2025 | 40370256 |
| 417 | 19 | 0.9891 | Site-specific integration of genes into hot spots for recombination flanking aadA in Tn21 transposons. Tn21-related transposons are widespread among bacteria and carry various resistance determinants at preferential sites, hs1 and hs2. In an in vivo integrative recombination assay it was demonstrated that these hot spots direct the integration of aminoglycoside resistance genes like aadB from Klebsiella pneumoniae and aacAI from Serratia marcescens, in a recA- background. The maximum required recognition sequence which must be present in both the donor and recipient plasmids is 5' CTAAAACAAAGTTA 3' (hs2). The double-site-specific recombination occurred with a frequency of 10(-5)-10(-6). The resulting structures include not only replicon fusion products but also more complex structures carrying two copies of the donor plasmid or simply the donor gene flanked by hs elements. hs1 and hs2 are thought to act as recognition sites for a transacting site-specific recombinase. By the use of Tn21 deletion derivatives, it has been shown that the recombinase is not encoded by Tn21. This new integrative recombination system is involved in the acquisition of new genes by Tn21-related transposons and their spread among bacterial populations. | 1991 | 1654505 |