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), respectively. 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.