Worm Breeder's Gazette 9(3): 64

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.

tRNATrp Suppressors of C. elegans

K. Kondo, J.A. Hodgkin, J. Gallante and B. Waterston

Figure 1

C. ve tRNATrP genes as determined by 
Southern blot analysis and DNA sequencing. Only three of these genes 
were found to be mutable to amber suppressors in prior studies: sup-5, 
.A.S. 81: 6784, 1984) and sup-24(st354) IV(wsG,9,
#1:48). The suppressor alleles allow the expression of that member of 
the gene family to be evaluated genetically, and tests with the three 
genes above show that sup-7 is the strongest of the three and sup-24 
is the weakest when tested against unc- 13(amber).
Extensive reversion analysis of unc-13(e1091);dpy-18(e364) using the 
mutagens EMS and NTG failed to identify any new tRNATrp supressor 
genes as detailed in the table below. Gene assignments were made on 
the basis of Southern blot analysis, as altering a tRNATrP gene to an 
amber suppressor creates an XbaI site in the anticodon loop.
{Figure 1}
Prior studies of amber alleles of tra-3(e1107,e1525 or e1903) IV (J.
A.H. Genetics 111:287, 1985) identified nine Informational suppressors.
of these one was genetically identified as sup-5 and the others were 
assigned on the basis of linkage data to three loci: sup-21 X(five 
isolates), sup-22 IV(two isolates) and sup-23 IV(one isolate). 
Southern analyses of the eight non-sup-5 isolates show that two of 
them are correlated with the creation of a new XbaI site in a tRNATrP 
gene containing fragment, which strongly suggests that they are 
tRNATrP suppressors. Since the other six isolates tested did not show 
any change in the XbaI pattern, the tRNATrP suppressors has been 
assigned to new loci, designated sup-28(e2058) and sup-29(e1986), 
The complete DNA sequence of five members of the family has been 
determined including sup-7, ion, 
by using a synthetic oligomer complimentary to the 3' end of the 
tRNATrP sequence we have examined the 5' half of the structural genes 
and 5' flanking sequence of the wild type alleles of the other seven 
genes. The structural parts so far determined are all identical, 
except for one gene which has a G19 to A19 change(P.N.A.S. 81:6784) 
and does not correspond to any of the five genes with amber suppressor 
activity. The 5' flanking sequences show at most only limited homology.

Comparison of suppressor efficiency in cross suppression tests have 
been made. Even two doses of sup-28 do not suppress the unc-13(amber) 
phenotype appreciably, in agreement with our failure to find sup-28 
isolates in our reversion analyses of unc-13(e1091). 
tly suppresses unc-13(e450 or 1091) in two 
doses and even one dose gives easily detectable suppression. In 
contrast, sup-28 and sup-S both efficiently suppress dpy-20(e2017) in 
two doses, but sup-S/+ is definitely weaker than two doses of sup-28. 
both suppressors have identical wild type structural gene sequences. 
These results suggest tissue specific differences of expression for 
these two tRNATrP genes.

Figure 1