rig was originally isolated from a rat insulinoma-derived cDNA library. The 145 amino acid sequence of the rig protein is invariant in mammalian cDNAs. In this paper, we have isolated the cDNA and genomic clones for yeast (Saccharomyces cerevisae) rig, determined their nucleotide sequences, and identified the gene product. The gene and the mRNA encode a basic protein of 142 amino acids which has 61.3% amino acid identity with mammalian rig protein. On two-dimensional gel electrophoresis, the in vitro transcription/translation product of yeast rig cDNA co-migrated with yeast ribosomal protein S21. These results led to the conclusion that yeast rig encodes ribosomal protein S21 and to the determination of the previously unknown primary structure of yeast S21 protein. Unlike most ribosomal protein genes of S. cerevisiae, the gene exists as a single copy in a haploid set of the yeast genome and has no intron, locating at chromosome VII or XV.
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