THE TRANSLATIONAL FUNCTION OF NUCLEOTIDE C1054 IN THE SMALL-SUBUNIT RIBOSOMAL-RNA IS CONSERVED THROUGHOUT EVOLUTION - GENETIC-EVIDENCE IN YEAST

Mutations at position C1054 of 16S rRNA have previously been shown to cause translational suppression in Escherichia coil. To examine the ef fects of similar mutations in a eukaryote, all three possible base sub stitutions and a base deletion were generated at the position of Sacch aromyces cerevisiae 18S rRNA corresponding to E. coil C1054. In yeast, as in E. coil, both C1054A (rdn-1A) and C1054G (rdn-1G) caused domina nt nonsense suppression. Yeast C1054U (rdn-1T) was a recessive antisup pressor, while yeast C1054 Delta (rdn-1 Delta) led to recessive lethal ity. Both C1054U and two previously described yeast 18S rRNA antisuppr essor mutations, G517A (rdn-2) and U912C (rdn-4), inhibited codon-nons pecific suppression caused by mutations in eukaryotic release factors, sup45 and sup35. However, among these only C1054U inhibited UAA-speci fic suppression caused by a UAA-decoding mutant tRNA(Gln) (SLT3). Our data implicate eukaryotic C1054 in translational termination, thus sug gesting that its function is conserved throughout evolution despite th e divergence of nearby nucleotide sequences.