Charlotte Walters

Charlotte Walters

Smith College

Biochemistry


1996

Mentor: John Collins, Ph.D. - Associate Professor of Biochemistry

Excision of Tc5: Double Stranded Gaps and their Repair

Tc5 is the most recently identified transposable element in the nematode Caenorhabditis elegans. The precise mechanism by which Tc5 excises from the sites it occupies in the genome is not well understood. This study considers the fate of the empty site left behind when Tc5 leaves. A genetic approach was used to test the hypothesis that Tc5 excision generates a double-stranded gap in the chromosome at its excision site. The gap could subsequently be repaired by a template-dependent process, as previously demonstrated for the elements Tc1 in C. elegans and P elements in Drosophila.

The rate of Tc5 excision was also determined. We found that: 1) when present in a heteroallelic form, reversion increases for an unc-22::Tc5 allele. 2) These revertants have a wild type sequence at the Tc5 excision site, i.e. no resulting footprint.

The heteroallelic form consisted of a deleted sequence on one of the unc-22 alleles and a Tc5 insertion on the other. The deleted sequence was in a region distant to the Tc5 insertion. By constructing this heteroallelic unc-22 mutant exhibiting the typical unc-22 mutant phenotype, singly picking these animals to a new petri plate, and allowing them to self fertilize, a frequency of revertant animals can be obtained. A high frequency of revertants and no footprints support the idea that Tc5 excision and the resulting double-stranded gap and repair process occur by the same mechanism as for Tc1.

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