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Transposition of IS1 circles.
1Institute of Molecular and Cellular Biosciences, the University of Tokyo, Bunkyo-ku, Tokyo 113-0032, Japan.
Genes to Cells : Devoted to Molecular & Cellular Mechanisms
|December 3, 1999
Summary
Bacterial IS1 circles, acting as transposition intermediates, facilitate high-frequency insertion into target DNA. This process, involving transposase and inducing the SOS response, is influenced by spacer length and H-NS protein.
Area of Science:
- Molecular Biology
- Bacterial Genetics
Background:
- IS1 is the smallest active transposable element in bacteria, encoding transposase.
- IS1 transposase mediates transposition, miniplasmid formation, and IS1 circle generation.
- The biological role of IS1 circles, comprising the IS1 sequence and a short spacer, was previously unknown.
Purpose of the Study:
- To investigate the biological significance and transposition mechanism of IS1 circles.
- To determine the role of spacer length and host factors in IS1 circle transposition.
Main Methods:
- Transposition assays using plasmids carrying IS1 circles with varying spacer lengths.
- Co-residence of plasmids to provide transposase.
- Analysis of transposition products and induction of the SOS response.
- Transposition experiments in strains deficient in H-NS.
Main Results:
- IS1 circles with short spacers (6-9 bp) transposed to target plasmids at high frequency.
- Transposition resulted in insertion of the donor plasmid, removal of the spacer, and target sequence duplication.
- Transposition frequency decreased with longer spacer sequences.
- Transposase encoded by IS1 circles induced the SOS response.
- IS1 circles transposed efficiently in H-NS-deficient strains.
Conclusions:
- IS1 circles function as intermediates in simple DNA insertion, with cleavage inducing the SOS response.
- H-NS protein may be involved in assembling the active IS1 DNA-transposase complex at the inverted repeats.