Host processing of branched DNA intermediates is involved in targeted transposition of IS911.
A simplified system using bacterial insertion sequence IS911 has been developed to investigate targeted insertion next to DNA sequences resembling IS ends. We show here that these IR-targeted events occur by an unusual mechanism. In the circular IS911 transposition intermediate the two IRs are abutted to form an IR/IR junction. IR-targeted insertion involves transfer of a single end of the junction to the target IR to generate a branched DNA structure. The single-end transfer (SET) intermediate, but not the final insertion product, can be detected in an in vitro reaction. SET intermediates must be processed by the bacterial host to obtain the final insertion products. Sequence analysis of these IR-targeted insertion products and of those obtained in vivo revealed high levels of DNA sequence conversion in which mutations from one IR were transferred to another. These sequence changes cannot be explained by the classic transposition pathway. A model is presented in which the four-way Holliday-like junction created by SET is processed by host-mediated branch migration, resolution, repair and replication. This pathway resembles those described for processing other branched DNA structures such as stalled replication forks.
Loot
Celine
C
Laboratoire de Microbiologie et Génétique Moléculaires, CNRS UMR5100, 118 Rte de Narbonne, F31062 Toulouse, France.
Turlan
Catherine
C
Chandler
Michael
M
D004251:DNA Transposable Elements / Q000235:genetics*; D004269:DNA, Bacterial / Q000235:genetics*; D004926:Escherichia coli / Q000235:genetics*; D029968:Escherichia coli Proteins / Q000235:genetics*; D008957:Models, Genetic; D016254:Mutagenesis, Insertional; D009693:Nucleic Acid Hybridization; D010957:Plasmids / Q000235:genetics
D004251:DNA Transposable Elements; D004269:DNA, Bacterial; D029968:Escherichia coli Proteins