Worm Breeder's Gazette 11(5): 34

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.

Amber-Suppressible Alleles That Are Not Amber Mutations

Greg Beitel and Bob Horvitz

Figure 1

We have reported that the five let-60 dominant multivulva (Muv) 
mutations (formerly known as lin-34 dominant Muv mutations) are amber 
suppressible (Beitel et al., Nature 348:1990).  For example 93% of let-
60(n1046) animals are Muv, while 11% of let-60(n1046); )
animals are Muv.  Using the genomic sequence of let-60 generously 
provided by Min Han and Paul Sternberg (Cell 63:1990), we sequenced 
the entire let-60 open reading frame of all five let-60 Muv alleles.  
These alleles all contain the identical G -> A transition mutation 
that results in a Glu for Gly substitution at amino acid 13.  The stop 
codon at the end of the coding sequence of both the wildtype and 
mutant alleles is not an amber codon.  Thus, it is not obvious why 
these mutations are amber-suppressible.  We suspect that the 
suppression is indirect and involves changes in the animal's general 
physiology or changes in the level or nature of a gene product(s) that 
is involved in let-60 function.  The former interpretation is 
supported by the ability of the apparently unrelated mutations unc-22(
e66) and lon-2(e678) to decrease the penetrance of the Muv phenotype 
and for dpy-20(e1282) to increase the penetrance of the Muv phenotype (
see below).  While there is no reason to expect that amber suppressors 
will often cause indirect suppression, our results reaffirm the need 
for prudence in interpreting results of suppression studies.
[See Figure 1]

Figure 1