Switching from cut-and-paste to replicative Tn7 transposition.
The bacterial transposon Tn7 usually moves through a cut-and-paste mechanism whereby the transposon is excised from a donor site and joined to a target site to form a simple insertion. The transposon was converted to a replicative element that generated plasmid fusions in vitro and cointegrate products in vivo. This switch was a consequence of the separation of 5'- and 3'-end processing reactions of Tn7 transposition as demonstrated by the consequences of a single amino acid alteration in an element-encoded protein essential for normal cut-and-paste transposition. The mutation specifically blocked cleavage of the 5' strand at each transposon end without disturbing the breakage and joining on the 3' strand, producing a fusion (the Shapiro Intermediate) that resulted in replicative transposition. The ability of Tn7 recombination products to serve as substrates for both the limited gap repair required to complete cut-and-paste transposition and the extensive DNA replication involved in cointegrate formation suggests a remarkable plasticity in Tn7's recruitment of host repair and replication functions.
May
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Howard Hughes Medical Institute, Johns Hopkins University School of Medicine, Baltimore, MD 21205 USA.
Craig
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D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D004260:DNA Repair; D004261:DNA Replication; D004251:DNA Transposable Elements / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins; D016297:Mutagenesis, Site-Directed; D010957:Plasmids; D017354:Point Mutation; D011995:Recombination, Genetic
D001426:Bacterial Proteins; D004251:DNA Transposable Elements; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; C098908:TnsA protein, E coli