Worm Breeder's Gazette 7(2): 52

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Complementation Pattern of cha-1 and unc-17 Alleles

J. Rand

Figure 1

The gene cha-1 IV is the structural gene for choline 
acetyltransferase (ChAT) and maps very close to unc-17.  Both cha-1 
and unc-17 mutants have a wide range of phenotypes in common, 
including uncoordinated behavior (coily and jerky when backing up), 
slow growth, small size, and most importantly, resistance to a wide 
range of cholinesterase inhibitors.  The evidence for two genes 
instead of one was: a) the cha-1 alleles that were tested all 
complemented unc-17 (e245) for the uncoordinated phenotype, and b) 
animals homozygous for e245 had normal ChAT levels.  We have also been 
able to separate cha-1 (p1152) from unc-17 (e245) by recombination; 
p1152 is 0.01-0.02% to the left of e245, but such a low recombination 
frequency could be due to intragenic as well as intergenic events.  We 
have now almost finished the complete complementation matrix for the 
uncoordinated phenotype of our cha-1 strains and the Cambridge unc-17 
strains.  Most of the alleles fall into one of two disjoint 
complementation groups, but there are three anomalies: p1156 (
originally isolated as being cha-1) and e113 and e876 (both isolated 
as unc-17) appear to be members of both complementation groups.  A 
clear prediction from the complementation pattern was that animals 
homozygous for e113 or e876 would lack ChAT (we already knew that 
p1156 had very low ChAT), but enzyme assays showed that all the unc-17 
strains, including e113 and e876 homozygotes, had between 60 and 150% 
of the wild-type ChAT activity.  At the moment, then, we have two 
overlapping complementation groups, with a lack of uniformity in the 
overlap set.  We have been considering various models, including a 
protein with two discrete, independently functioning domains, or a 
deletion hotspot located between two adjacent genes, or even 
overlapping genes.  Next on the agenda is careful biochemical analysis 
of ChAT from the unc-17 strains.
[See Figure 1]

Figure 1