Worm Breeder's Gazette 8(3): 86
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
Our studies on unc-22 and those of D. Eide and P. Anderson on unc- 54 suggest that high Tc1 copy number per se is not sufficient to induce transposition. However, we also know from our genetic studies on unstable unc-22 mutations that transposition into unc-22 is probably controlled by more than one region present in the BO strain ( Moerman and Waterston, Genetics in press). In light of these two observations we are attempting to isolate a transposition 'factor'. Here we use factor as it has been described for P in D. melanogaster. To monitor the activity of such a factor we have used the reversion frequency of an unstable unc-22 mutation, st136. In the BO strain, RW7002, st136 reverts at a frequency of 2 x 10+E-3, but in RW7012, a primarily Bristol derivative of RW7002, st136 reverts at a frequency of less than 10+E-7. We have constructed 12 isogenic strains of mixed Bristol-Bergerac genomes from hybrids of RW7012 and BO, and these strains exhibit a range of reversion frequencies from about 10+E-3 to probably less than 10+E-6. The observation of a rather large 'low reversion frequency' class, about 25% of the strains, suggested there may actually be very few factors. An attractive hypothesis is that the factors may be a subset of the Tc1 elements present in BO. We examined these new st136 Bristol- Bergerac strains for Tc1 copy number, and found them to differ by as much as 3-fold. No correlation between a strains Tc1 copy number and its reversion frequency was observed. One strain, RW7037, has a relatively low Tc1 copy number (tentatively less than 100 copies) and also a high reversion frequency. We think it may be possible to use derivatives of RW7037 to map genetically a single factor. If we are lucky this factor will be homologous to Tc1.