Worm Breeder's Gazette 10(2): 30

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The Continuing Saga of Morpho-mab Suppression: Suppression of a 3' Deletion Mutant of unc-54

Jonathan Hodgkin

Figure 1

In the previous issue of the gazette (WBG 10-1:70), R. P.  and P. A. 
reported suppressor mutations that act in an allele-specific manner 
on a spontaneous mutation of unc-54.  This mutation, r293, carries a 
deletion of about 250 bp in the 3' noncoding portion of the gene, that 
includes the AAUAAA sequence but does not appear to alter the coding 
The properties of the extragenic suppressors of r293 suggested that 
they might be members of the class of pleiotropic suppressors 
identified by reversion of certain alleles of tra-2 and lin-29 (J. H., 
A.  Papp & V.  Ambros, WBG 10-1:112).  Complementation tests showed 
that three of the five complementation groups identified by r293 
suppression correspond to the known morpho-mab suppressor genes mab-1, 
ll five classes of r293 
suppressor exhibit the characteristic morphological abnormalities of 
male bursa and hermaphrodite vulva.  The two new complementation 
groups were mapped to LGI and LGIII on the basis of this phenotype, 
and given the names mab-15 and mab-16.  Both mab-15(r860) and mab-16(
r896) are able to suppress the sensitive allele of tra-2, e1209.  
Conversely, mab-14(mal16), which was detected as a suppressor of lin-
29(n546) but not picked up in the r293 reversion, is able to suppress 
r293.  The isolation table below suggests that mab-1 and mab-11 are 
frequent mutations (and they appear to be found at approximately gene 
knockout frequency), but the other four are represented only by rarer 
The nature of the r293 mutation may indicate that suppression by the 
morpho-mabs acts at the level of RNA rather than protein.  Molecular 
analysis of unc-54 transcripts in r293 and its revertants should 
clarify the mechanism.  It is likely that the morpho-mab suppression 
identifies a distinct class of allele in a variety of otherwise 
unrelated genes, in which case it may be a useful diagnostic tool.
[See Figure 1]

Figure 1