| Co-Investigator(Kenkyū-buntansha) |
SEKINE Yasuhiko Rikkyo University, Cdege of Science, Assistant Professor, 理学部, 助教授 (80222074)
OHTSOBO Hisako The University of Tokyo, Institute of Molecular and Celular Biosciences, Leclurer, 分子細胞生物学研究所, 講師 (20158801)
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| Research Abstract |
Transposons are mobile DNA elements and encode transposases required for their transposition. These elements cause various genomic rearrangements by their ability to transpose. This study is aimed at elucidation of molecular mechanisms of transposition promoted by bacterial insertion elements IS1 and IS3 and the ampicillin-resistance transposon Tn3, which are supposed to transpose in a different mode. We have previously shown that a circular IS3 molecule is generated from the IS3-carrying plasmid and is converted to a linear molecule, which is inserted into a new target site. We showed here that the IS3 transposase binds to terminal inverted repeats (IR) and that an IR end is cleaved and transferred to the other end to give a characteristic figure-8 molecule in a complex consisting of two transposases and two IRs. complex is formed by binding of each transposase to a domain (named A) in one IR, as well as to the other domain (named B) in the other IR. As for IS1, we showed that IS1 requires a host protein H-NS unlike IS3, and that IS1 transposase has a catalytic D-D-E motif in the C-terminal region, as well as two IR-binding motifs (helix-turn-helix and Zinc-finger) in the N-terminal region unlike the IS3 transposase. As for Tn3, we showed that nicking, the first reaction of transposition, at the 3' end of IR requires acyl carrier protein from the host, which promotes the formation of a transposase-IR complex. Furthermore, we identified IS elements present in the genomes of Escherichia coli strains and their plasmids and found that they are involved in generation of mutations, such as insertions, deletions, and substitutions, and that these mutations are useful to determine phylogenetic relationships among various pathogenic E. coli strains.
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