Worm Breeder's Gazette 9(1): 30

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.

Isolation of mec mutants in TR679

J. Srinivasan, J. Mindich, R. Goldstein, and M. Chalfie

Figure 1

We have isolated nineteen mec mutants from the mut(r459) strain 
TR679 (kindly provided by Phil Anderson).  Mutants were picked at 20 C 
from plates grown from strips from dauered plates.  When a mutant was 
found, all plates from the same dauered plate were discarded.  Sets of 
plates that yielded no mutants were used as sources of additional 
dauers for the next rounds of screening.  Thus, each mutant was 
presumed to be an independent isolate (but see below).
As seen in the accompanying table, the distribution and relative 
frequency of these spontaneous mutations were different from those of 
mutations arising from EMS mutagenesis.
[See Figure 1]
In addition, no spontaneous mutations have been identified yet in 
mec-5 or mec-7, genes that are readily mutated by EMS (freq.  = 3.3 X 
10+E-4) and 2.3 X 10+E-4) respectively; many of the mec-5 alleles are 
ts, but the frequency of EMS mutation at 15 C is still 0.9 X 10+E-4).
Three of the spontaneous mec mutations, mec-1(u295), 
5), and mec-4 (u348) reverted spontaneously.  A 
fourth mutation, mec-3(u300), that appears to have a copy of Tc1 
inserted in the gene (see Way and Chalfie in this 'newsletter) did not 
revert (150,000 chromosomes examined).
We are examining the Tc1 patterns in these mutants.
A caution: We cannot be certain that all of the spontaneous mec 
mutations are independent.  If a mec mutation arose on a chromosome 
carrying a lethal mutation, it may remain cryptic in the population.  
Because of the subculturing used in our screening, this could mean 
that the same mec mutation could populate a number of presumably 
independent plates.  Thus, at this time we do not know whether all of 
the mec mutations are independent.  In these experiments, we did two 
mass screenings of TR679, each from a different stock from Wisconsin.  
All nine mec-9 mutations came from the first screening, yet a screen 
by complementation for a cryptic mec-9 allele was unsuccessful.  We 
feel, however, that at least two mutations in mec-1 and mec-4 and 
three of the mec-3 mutations are independent.  It seems that a better 
way to determine the frequency of spontaneous mutations would be by 
precomplementation screening.

Figure 1