Worm Breeder's Gazette 8(2): 45

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Another Amber Suppressor: sup-21(e1957) X

J. Hodgkin

Figure 1

The mutation e1903 (isolated by Ed Hedgecock) is a leaky amber 
allele of tra-3 IV.  At 15 C, tra-3(e1903)XX animals are intersexual 
and sometimes self-fertile; at higher temperatures they exhibit the 
usual Tra-3 phenotype, being partly masculinized and sterile.  It is 
possible (with patience) to grow up large populations of homozygous 
e1903 animals at 15 C.  These populations were mutagenized with EMS 
and grown for a further period at 15 C.  The fertility of the animals 
is so low that there is strong selection for reversion of the Tra-3 
phenotype.  Three good suppressors were obtained in this way, out of a 
total of ca. 10+E5 mutagenized genomes: e1957, e1958, e1986.  All 
three are dominant suppressors of two tra-3 amber alleles, e1903 and 
e1107, but have no effect on a non-amber allele, e1767.  They differ 
in the strength of suppression: e1957 > e1958 > e1986.  Two are sex-
linked: e1957 was mapped to a locus (designated sup-21) about 2% right 
of dpy-6.  The map location of e1958 is similar or identical, while 
e1986 maps to LGIV.  I have compared the spectrum of suppression by 
sup-21(e1957) with that of sup-5 and sup-7, the amber suppressors 
identified by Bob Waterston (see Table below).  It appears that sup-21 
is a consistently weaker suppressor than sup-5.  However, it is 
surprising that it should have absolutely no effect on the unc-13 
alleles e450 and e1091, which are well suppressed by sup-5.  It is 
unlikely that this reflects tissue specific suppression by sup-21, 
because the unc-13 allele e312 does respond slightly.  A possible 
explanation is that sup-21 suppression results in the insertion of a 
different amino acid from that inserted by sup-5 (i.e, not tryptophan).

[see Figure 1]

Figure 1