Worm Breeder's Gazette 9(2): 18

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.

More Sequenced unc-54 Mutations

J. Kiff, D. Moerman, and B. Waterston

We have sequenced three additional missense alleles of unc-54 that 
suppress unc-22 induced twitching.  One, st134, is a member of the s74-
like class while two others, st130 and st132 appear to define a new 
class of mutation in unc-54.  These latter mutations not only allow 
for dominant suppression of unc-22 induced twitching, but, in addition,
as homozygotes have significant A-band disorganization.
The change in st134 is TCC (ser) to TTC (phe) at position 2338, 
which makes this allele the 5'-most sequenced mutation in unc-54.  
Most intriguing, st134 is only two base pairs away from s95 which is 
at position 2340 (i.e., these two mutations are in adjacent residues). 
This observation, together with the reversion studies of s95 which we 
described in the last Newsletter, suggests that these two residues are 
essential for myosin head activity.  The precise biochemical role of 
the region is unknown, but it is intriguing that these mutations lie 
very close to the putative ATP-binding domain.
The change in st132 is GAG (glu) to AAG (lys) at position 3646 and 
in st130 it is TGT (cys) to TAT (tyr) at position 3739.  These two 
mutations lie in the S1 region of the molecule.  The observation that 
alterations in this region of the molecule can affect thick filament 
structure as well as the contraction/relaxation cycle is surprising.  
Previously, the rod has been thought to have the primary role in thick 
filament assembly and integrity.  The stage of thick filament assembly 
or maintenance affected by these mutations is unknown.  However, 
second site compensatory mutations have been isolated (see previous 
Newsletter) and using these, it may be possible to determine if st130 
and st132 affect the organization of the thick filament through 
interactions with either the hinge or the rod portion of the molecule.