Worm Breeder's Gazette 11(5): 95

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More on unc-101

Junho Lee, Gregg Jongeward and Paul Sternberg

Figure 1

unc-101 mutations confer an Unc phenotype and suppress the vulval 
defect of weak let-23 alleles.  We are interested in the genetics and 
molecular biology of this locus because of its broad range of 
phenotypes and interaction with let-23.We have attempted to identify a 
null allele of unc-101.  We have used trimethyl-psoralen (TMP), which 
produces small deletions at high frequency (Edgar et al.  WBG 11(2) 79)
, as a mutagen in a screen for mutations that fail to complement unc-
101(rh6).  Out of 11,000 F1 cross-progeny hermaphrodites, one new 
allele, sy216, was recovered.  This allele is a homozygous lethal.  
sy216 homozygotes arrest in the L1 stage but remain alive for 5-6 days.
The lethality of other alleles can be rescued by maternal expression,
but the lethality of sy216 cannot be rescued, since no Dpy segregate from dpy-5(e61) 
y216)/++ heterozygous hermaphrodites.  Because this 
allele is more severe than the existing 6 unc-101 alleles, we consider 
this allele a putative null allele of unc-101.  sy216 does not delete 
unc-75, it overlap eDf3.  We 
still do not know whether this mutation is a point mutation in unc-101 
or a deletion of unc-101 and as yet unidentified flanking gene(s).
We have tried to find extragenic suppressors of unc-101.  We 
screened the F2 progeny of 20,000 EMS mutagenized F1 chromosome sets 
of unc-101(sy108) and dpy-5(e61)h6) and have not 
recovered any candidates.
We are currently trying to clone unc-101 using parallel RFLP mapping 
with the congenic strain used for cloning ced-1 (Gerber et al.  WBG 11(
4) 24) which was kindly provided by Bob Horvitz's lab.
Further mapping of unc-101 places it to the left of let-201, let-202,
let-203 and the left end of eDf3.  Therefore unc-101 is not a 
recessive hypermorph, which we had previously suggested.
[See Figure 1]

Figure 1