[Immunity to repeated transposition of the insertion sequence IS21]
Molekuliarnaia Biologiia
|September 1, 1985
Summary
Plasmids with IS21 elements show reduced IS21 transposition but enhance bacterial chromosome insertion. This study investigates IS21 transposition immunity mechanisms.
Area of Science:
- Molecular Biology
- Genetics
- Microbiology
Background:
- The IS21 element is a mobile genetic element with known transposition capabilities.
- Understanding transposition mechanisms is crucial for comprehending genome dynamics and evolution.
- Previous studies have explored transposition immunity, but the role of IS21 in this phenomenon requires further elucidation.
Purpose of the Study:
- To investigate the transposition of the IS21 element into pBR325 derivatives.
- To determine the effect of IS21 presence and localization on its own transposition frequency.
- To assess the influence of IS21-carrying plasmids on the transposition of another element (pRP19.6) into the bacterial chromosome.
Main Methods:
- Construction of pBR325 derivatives containing a single copy of the IS21 element at different locations.
- Study of IS21 transposition into these derivatives using plasmid pRP19.6, a temperature-sensitive mutant.
- Restriction endonuclease analysis to characterize the structure of resulting plasmids.
- Quantification of pRP19.6 insertion frequency into the bacterial chromosome in the presence of pBR325::IS21 derivatives.
Main Results:
- Transposition frequency of IS21 into pBR325 derivatives was significantly lower (by two orders of magnitude) compared to the parental pBR325 plasmid.
- Insertion of a second IS21 copy into pBR325 derivatives resulted in the formation of tandem repeated copies.
- Plasmids carrying IS21 (pBR325::IS21) increased the frequency of pRP19.6 insertion into the bacterial chromosome by 3-9 to 200-300 times, depending on IS21 localization.
Conclusions:
- The presence of IS21 on plasmids confers a form of transposition immunity, reducing further IS21 transposition.
- IS21-carrying plasmids can act as enhancers for the transposition of other genetic elements to the bacterial chromosome.
- The findings provide insights into the complex mechanisms governing transposition immunity and inter-element interactions in bacteria.
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