Worm Breeder's Gazette 9(1): 29

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.

Elevated Levels of Tc1 Transposition and Excision in Mutator Strains

P. Anderson, B. Saari, and J. Collins

At the meetings in May, we reported the isolation of mutator (mut) 
strains that exhibit elevated frequencies of spontaneous Tc1 excision 
and transposition (Abstracts of the 1985 CSH Meeting).  These mutants 
were isolated because they exhibit elevated frequencies of reversion 
to wild type of an unc-54 ::Tc1 mutant.  Southern blots indicate that 
mutator-induced Unc-54+ revertants contain precise or nearly precise 
excisions of Tc1 from unc-54.  Individual mutator strains (we have 8 
independent isolates) have frequencies of Unc-54+ reversion that are 
increased 10- to 200-fold above their non-mutator parent.
Each of the mutator strains also exhibits elevated frequencies of 
TcI transposition.  For individual mutator strains, the frequencies of 
spontaneous unc-22 mutants (twitchers) obtained was 7- to 50-fold 
greater than in the non-mutator parent.  The strongest of our mutator 
strains have unc-22 mutation frequencies of approximately 2 x 10+E-3.  
All tested mutator-induced unc-22 mutants are unstable, reverting to 
wild type at frequencies in excess of 10+E-3.
Southern blots demonstrate that the majority (13/17) of mutator 
induced unc-22 mutants contain ~1.6 kb insertions in unc-22 (presumed 
to be Tc1).  Of the remaining four, two contain as yet uncharacterized 
DNA rearrangements in the unc-22 region, and two appear unchanged from 
wild type.  Southern blots also confirm that all tested mutator-
induced unc-22+ revertants contain precise or nearly precise excisions 
of Tc1 from unc-22.Each of the mutators exhibits a semi-dominant Him (
high incidence of males) phenotype.  The Him phenotypes of four 
mutator induced mutants have been mapped.  Three are linked to unc-54 I.
For one of these three (mut-3(r456), contained in strain TR638) the 
mutator phenotype is also linked to unc-54 I.  (The Mut phenotype is 
defined as elevated frequencies of reversion of Tc1-induced mutants.)  
The Him phenotype of the fourth mutator (mut-2(r459), contained in the 
ever-popular strain TR679) is linked to dpy-10 II.  The mutator and 
the Him phenotype of TR679 generally cosegregate in crosses, so we 
anticipate that the mutator phenotype will also map to LGII.  
Experiments to demonstrate this are in progress.