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.

A Needle in a Haystack?

I. Mori, D. Moerman, R. Waterston

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.