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.
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.