Nucleotide sequence of the SUF2 frameshift suppressor gene of Saccharomyces cerevisiae.

To elucidate the molecular mechanism of frameshift suppression by the SUF2 gene of yeast, the sequences of DNA fragments carrying the SUF2-1 and suf2+ alleles of the gene and surrounding regions have been determined. Comparison of the suppressor and wild-type sequences indicates that the SUF2 gene product is a proline tRNA. Disregarding possible base modifications, we find that the wild-type suf2+ anticodon of the tRNA inferred from the DNA sequence is 3'-GGA-5'. The SUF2-1 mutation represents the insertion of a G-C base pair at a position in the gene that corresponds to the anticodon loop of the tRNA. Replacement of the wild-type suf2+ anticodon by a 3'-GGGA-5' fourbase anticodon enables the SUF2-1 tRNA to suppress the 5'-CCCU-3' four-base codons generated as the result of the his4-712 and his4-713 frameshift mutations. This nontriplet codon-anticodon interaction restores the correct reading frame and allows synthesis of a functional his4 protein.