Worm Breeder's Gazette 9(3): 37

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.

A Screen for Recessive Lethals in the unc-60(V) Region

K.S. McKim, M.F.P. Heschl, R.E. Rosenbluth and D.L. Baillie

The analysis of the left end of LGV has included the fine structure 
analysis of the unc-60 gene, in which we found this gene to be 
approximately 0.007-0.014 mu. across (WBG Vol. 9(2)). We have now 
analyzed other complementation groups near the unc-60 gene. The basic 
idea was to screen heterozygous (unc-60/+) worms for closely linked 
lethal mutations. The dpy-11 marker was positioned cis to unc-60 to 
facilitate subsequent three factor mapping. This chromosome was 
balanced over the deficiency sDf26, which deletes most of the region 
between unc-60 and dpy-11. The deficiency serves two purposes; l) as a 
balancer suppressing recombination 2) and to select against mutations 
not tightly linked to unc-60 or to dpy-11We screened 1222 0.012M EMS 
treated chromosomes and recovered 13 lethal mutations. We positioned 
the lethals relative to unc-60 and dpy-11 by three factor mapping. The 
mutations were then balanced over eT1(III,V) and complementation 
tested against the set of deficiencies for LGV left (see WBG 9(2):81). 
Only two of the mutations mapped near unc-60. The rest mapped to the 
right within 1.7 mu. of dpy-11. This agrees with the observation that 
unc-60 is in a gene 'sparse' region on the recombination map (see CGC 
Of the 11 lethals that mapped to the dpy-11 region, one was a new 
deficiency (sDf35) in the unc-23-unc-42 region. Five more mapped to 
previously unidentified genes. Two of these five mapped outside the 
eT1 balanced region. Another mutation, s833, is the fourth EMS allele 
of let-333 while s825 is the fourth EMS allele of let-337; which maps 
close to dpy-11 (<0.5mu.). None of the mutants mapped between sDf-26 
and dpy-11.Both of the mutations near unc-60 mapped to its right. One 
of the mutations (s819) was found to be allelic to emb-29. This allele 
is the first non-ts allele of this gene and also positions emb-29 0.
4mu. to the right of unc-60. The second mutation defines a new gene, 
let-426(s826) and maps 1.1 mu. the right of unc-60. This type of 
screen, with a large deficiency like sDf26, appears to be useful for 
isolating mutations in a defined region.