Worm Breeder's Gazette 10(3): 14

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fem-3(gf) mutations are single base pair changes in the 3' untranslated region of fem-3

Julie Ahringer and Judith Kimble

Figure 1

The fem--3(+) gene specifies male development.  In XX hermaphrodites,
fem-3 is required only in the germline: it must first be active to 
direct spermatogenesis and then it must be packaged into oocytes for a 
maternal contribution to the embryo.  This maternal product must be 
negatively regulated so that it will not transform oocyte precursors 
into sperm.  Nine temperature sensitive gain-of-function (gf) alleles 
of fem-3 cause the aberrant production of a vast excess of sperm in 
hermaphrodites; no oocytes are made, and no alteration is observed in 
the hermaphrodite soma.  Genetic studies suggest that fem-3(gf) 
mutations do not increase fem-3(+) activity, but instead produce a 
novel unregulated product (1).  The germline-specific masculinization 
of fem-3(gf) is consistent with the finding that fem-3 RNA's are 
limited to the germline in hermaphrodites (2).  The wild-type fem-3 
gene has been cloned, and its sequence and gene structure elucidated (
2; Rosenquist, unpublished).  We have cloned all nine fem-3(gf) genes. 
We sequenced one fem-3(gf) allele, q20, in its entirety and found a 
single base pair change in the 3' untranslated region (3'-UTR).  
Partial sequencing of the rightmost eight fem-3(gf) alleles similarly 
reveal changes in the  3'-UTRs.  The two weak fem-3(gf) alleles are 
both T to C changes of the same base pair; the five intermediate fem-3(
gf) alleles are all C to T changes of an adjacent base pair; and the 
one strong fem-3(gf) allele is a G to T change a few bases pairs 3' of 
the other mutations (see figure).  One super strong fem-3(gf), q95, 
which is barely temperature sensitive, is a 114bp deletion centered 
around the region of the point mutants and contained within the 3'-UTR,
It may be significant that most of the fem-8(gf) mutants lie in a CTT 
repeat.  The short sequence in the 3'-UTR that has been shown by 
transformation experiments to be important to unc-54 function also 
contains a CTT repeat (Fire, WBG 10 No.  2); furthermore, this region 
is conserved in the 3'-UTR of the mlc-1 gene (Cummins and Anderson, 
pers .  comm.  ) .  The clustering of these fem-3(gf) base pair 
changes within a stretch of five base pairs indicates that this small 
region is centrally involved in the regulation of fem-3.  The 
temperature sensitivity of the mutations suggests the involvement of 
an RNA/RNA or RNA/protein interaction.  In searches for secondary 
structure in the region, there is no striking stem including or near 
the base pairs identified by mutation.  The negative regulation of fem-
3 activity identified by the  mutations may act through RNA stability, 
efficiency of translation, or localization of the RNA within the germ 

Figure 1