The duplicated Saccharomyces cerevisiae gene SSM1 encodes a eucaryotic homolog of the eubacterial and archaebacterial L1 ribosomal proteins.
A previously unknown Saccharomyces cerevisiae gene, SSM1a, was isolated by screening for high-copy-number suppressors of thermosensitive mutations in the RNA14 gene, which encodes a component from the polyadenylation complex. The SSM1 a gene codes for a 217-amino-acid protein, Ssm1p, which is significantly homologous to eubacterial and archaebacterial ribosomal proteins of the L1 family. Comparison of the Ssm1p amino acid sequence with that of eucaryotic polypeptides with unknown functions reveals that Ssm1p is the prototype of a new eucaryotic protein family. Biochemical analysis shows that Ssm1p is a structural protein that forms part of the largest 60S ribosomal subunit, which does not exist in a pool of free proteins. SSM1 a is duplicated. The second gene copy, SSM1b, is functional and codes for an identical and functionally interchangeable Ssm1p protein. In wild-type cells, SSM1b transcripts accumulate to twice the level of SSM1a transcripts, suggesting that SSM1b is responsible for the majority of the Ssm1p pool. Haploid cells lacking both SSM1 genes are inviable, demonstrating that, in contrast with its Escherichia coli homolog, Ssm1p is an essential ribosomal protein. Deletion of the most expressed SSM1b gene leads to a severe decrease in the level of SSM1 transcript, associated with a reduced growth rate. Polysome profile analysis suggests that the primary defect caused by the depletion in Ssm1p is at the level of translation initiation.
Petitjean
A
A
Centre de Génétique Moléculaire, Université Pierre et Marie Curie, Gif-sur-Yvette, France.
Bonneaud
N
N
Lacroute
F
F
D015720:5'-Nucleotidase; D000595:Amino Acid Sequence; D001105:Archaea / Q000235:genetics; D001483:Base Sequence; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000235:genetics; D005656:Fungal Proteins / Q000235:genetics*; D015870:Gene Expression; D005800:Genes, Fungal / Q000235:genetics*; D005804:Genes, Lethal / Q000235:genetics; D008969:Molecular Sequence Data; D005810:Multigene Family / Q000235:genetics*; D009708:Nucleotidases; D010442:Peptide Chain Initiation, Translational; D011132:Polyribosomes / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis; D012269:Ribosomal Proteins / Q000235:genetics*; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D013489:Suppression, Genetic; D039221:mRNA Cleavage and Polyadenylation Factors
D005656:Fungal Proteins; D012333:RNA, Messenger; D012269:Ribosomal Proteins; D029701:Saccharomyces cerevisiae Proteins; D039221:mRNA Cleavage and Polyadenylation Factors; C028546:ribosomal protein L1; C512638:RNA14 protein, S cerevisiae; D009708:Nucleotidases; D015720:5'-Nucleotidase; C489269:SDT1 protein, S cerevisiae