Worm Breeder's Gazette 9(3): 17

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.

Mutator Mapped

M. Finney and B. Horvitz

Transposition of Tc1 in Phil Anderson's mutator strains has proved 
useful in tagging a number of genes. It would be even more useful if 
the activity responsible for increased transposition were genetically 
defined, so that it could be easily moved into new backgrounds, and 
cloned, so that it could be used for DNA transformation.
We backcrossed TR674 (genotype mut-2 c1 and 
containing many Bergerac-derived copies of Tc1) three times to Bristol.
The resulting strain is called MT2878 and was used in all further 
We developed a new assay for Tc1 transposition that is faster and 
easier than unc-54 reversion. While working with MT2878 we isolated an 
allele of dpy-19 that confers a very weak Dpy phenotype. This allele 
is associated with an identified Tc1 insertion; when the Tc1 excises 
it often leaves behind strong dpy-19 alleles, possibly by imprecise 
excision. In a mutator background about 1-2% of gametes carry a strong 
dpy-19 allele; in non-mutator backgrounds the frequency is at least 50-
fold lower. Since the Weak Dpy animals are much healthier than Unc-54 
animals, they are easier to work with genetically and grow to large 
numbers very quickly.
Using both this assay and unc-54 reversion, we have mapped an 
activity from MT2878 sufficient to cause high level excision. It is 
located on LG I right of dpy-S, left of sup-17, and very close to unc-
13. This activity also causes new mutations (dpys, uncs, twitchers, 
etc.) even after it has been ten times backcrossed into Bristol.
A ten-times backcrossed strain which has mutator activity has about 
fifteen extra copies of Tc1. We are currently doing finer mapping to 
determine whether one or more of these Tc1s is required for mutator 
activity. In the mean time, the highly backcrossed strains are useful 
for looking for new Tc1-induced mutations because they are healthy and 
they have very few extra Tc1 copies.
Although 'hopping' activity in MT2878 clearly maps to LG I, it may 
map to other locations in other derivatives of TR674 if the activity 
is caused by a moveable element.