The mutation
mn4, which was identified among the progeny of X-ray treated males, confers a blistered phenotype. The mutation is dominant to wild-type with 100% penetrance. The reference allele for
bli-6 IV is
sc16, which is recessive to wild type. Meredith Kusch has mapped
mn4 and another dominant mutation,
sc74, close to
sc16; and Park and Horvitz (1986, Genetics 113:821) have mapped their EMS-induced dominant mutation
n776 very near to
sc16. Thus it appears that
bli-6 IV is represented by one recessive and three dominant alleles. We have identified 44 independent EMS-induced revertants of
mn4. All are extragenic suppressors, and they fall into two general classes: 23 are recessive dumpy mutations and 21 have wild-type morphology. All but one of the dumpy mutations have been assigned to known dpy genes, as follows: 1 allele of
dpy-1 III, 3 alleles of
dpy-3 X, 4 alleles of
dpy-4 IV, 3 alleles of
dpy-5 I, 3 alleles of
dpy-7 X, 4 alleles of dpy- 8 X, 1 allele of
dpy-9 IV, 1 allele of
dpy-10 II, and 2 alleles of dpy- 13 IV. Not all dumpy mutations suppress
mn4. For example,
dpy-6(
e14) X,
dpy-17(
e164) III and
dpy-18(
e364) III do not suppress
mn4 (and no suppressing alleles of these genes have been identified in our reversion screen), but
dpy-5(
e61) and
dpy-1O(
e128) do. All but three of the 23 dumpy mutations are recessive suppressors of
mn4, i.e., animals of genotype dpy/+;
mn4/+ are Bli non-Dpy. In the other three cases, however, dpy/+;
mn4/+ animals are non-Bli non-Dpy. The three dominant suppressors are alleles of
dpy-4, of these genes, we have at least one recessive suppressor allele; thus in each case the effect is allele specific, not gene specific. An incidental point about another dpy: Claire Kari has shown that the previously unmapped
dpy-12(
e182) is an allele of
dpy-3.Analysis of the wild-type suppressors has not progressed as far, although most have been outcrossed at least twice. Seven of the 21 suppressors are dominant, by the criterion that
mn4/+; sup/+ hermaphrodites are non- Bli (males of this genotype are sometimes blistered). Three of the recessive wild-type suppressors appear to be X-linked (
mn4/+; sup/O males are non-Bli) and fail to complement each other. We note that Kusch and Edgar (C. elegans Newsletter 9, no. 1. p.51) previously identified a wild-type suppressor of
bli-6(
sc73) which mapped to LGV and which also suppressed
bli-6(
sc16).We have put
mn4 into a TR679- like background and identified a few spontaneous revertants. One is a dumpy, an allele of
dpy-5 I, and we have a spontaneous revertant of it.