A SECOND INFORMATIONAL SUPPRESSOR, SUP-7 X, IN CAENORHABDITIS ELEGANS

More than 30 independent suppressor mutations have been obtained in the nematode C. elegans through reversion analysis of two unc-13 mutants. Many of the new isolates map to the region of the previously identified informational suppressor, sup-5 III (Waterston and Brenner 1978). Several of the other suppressor mutations map to the left half of the X-linkage group and define a second suppressor gene, sup-7 X. In tests against 40 mutations in six genes, the sup-7(st5) allele was found to suppress to a greater extent the same alleles acted on by sup-5(e1464). Like sup-5(e1464), sup-7(st5) acts on null alleles of the myosin heavy-chain gene unc-54 I (MacLeod et al. 1977; MacLeod, Waterston and Brenner 1977) and the putative paramyosin gene unc-15 I (Waterston et al. 1977). Chemical analysis of unc-15(e1214); sup-7(st5) animals show that paramyosin is restored to more than 30% of the wild-type level. —As was observed for sup-5(e1464), suppression by sup-7(st5) is dose dependent and is greater in animals grown at 15° than at 25°. However, associated with this increased suppression is a decreased viability of sup-7(st5) homozygotes. Reversion of the lethality has resulted in the isolation of deficiency mutations that complement st5 lethality, but lack suppressor function. These properties of sup-7(st5) suggest that it, like sup-5(e1464), is an informational suppressor of null alleles, and its reversion via deficiencies further narrows the possible explanations of its action.