RIBOSOMAL-PROTEIN L9 IS THE PRODUCT OF GRC5, A HOMOLOG OF THE PUTATIVE TUMOR-SUPPRESSOR QM IN SACCHAROMYCES-CEREVISIAE

Genes encoding members of the highly conserved QM family have been ide ntified in eukaryotic organisms from yeast to man. Results of previous studies have suggested roles for QM in control of cell growth and pro liferation, perhaps as a tumor suppressor, and in energy metabolism. W e identified recessive lethal alleles of the Saccharomyces cerevisiae QM homolog GRC5 that increased GCN4 expression when present in multipl e copies. These alleles encode truncated forms of the yeast QM protein Grc5p. Using a functional epitope-tagged GRC5 allele, we localized Gr c5p to a 60S fraction that contained the large ribosomal subunit. Two- dimensional gel analysis of highly purified yeast ribosomes indicated that Grc5p corresponds to 60S ribosomal protein L9. This identificatio n is consistent with the predicted physical characteristics of eukaryo tic QM proteins, the highly biased codon usage of GRC5, and the presen ce of putative Rap1p-binding sites in the 5' sequences of the yeast GR C5 gene. (C) 1997 John Wiley & Sons, Ltd.