ABSTRACT
A nucleotide sequence of the yeast Saccharomyces cerevisiae omnipotent suppressor SUP2 (SUP35) gene is presented. The sequence contains a single open reading frame (ORF) of 2055 bp, which may encode a 76.5-kDa protein. A single transcript of 2.3 kb corresponding to a complete ORF is found. Analysis of codon bias suggests that the SUP2 gene is not highly expressed. The C-terminal part of the deduced amino acid sequence shows a high homology to yeast elongation factor EF-1 alpha, whereas the N-terminal part is unique for the SUP2 protein. The N terminus contains a number of short repeating elements and possesses an unusual amino acid composition. Analysis of the nucleotide and deduced amino acid sequences indicates that three additional proteins could possibly be expressed, two of which might be initiated on internal ATG codons and a third might be formed by alternative splicing. One of these proteins is supposed to be imported into mitochondria. Possible functions of the SUP2 gene product(s), especially its putative activity as a soluble factor controlling the fidelity of translation, are discussed.
Subject(s)
DNA, Fungal , Genes, Fungal , Saccharomyces cerevisiae/genetics , Amino Acid Sequence , Amino Acids/analysis , Base Sequence , Chromosome Mapping , Cloning, Molecular , Codon , Fungal Proteins/physiology , Molecular Sequence Data , Nucleic Acid Hybridization , Plasmids , Protein Biosynthesis , RNA, Fungal , RNA, MessengerABSTRACT
A conditional respiratory deficiency in yeast Saccharomyces cerevisiae is expressed as a result of a nuclear mutation in sup1 and sup2 genes (II and IV chromosomes, respectively), coding for a component of cytoplasmic ribosomes (Ter-Avanesyan et al. 1982). One such strain is studied here in detail. The strain is temperature-dependent and expresses a respiratory deficient phenotype at 20 degrees C but not at 30 degrees C. Moreover, the strain is simultaneously chloramphenicol-dependent and is able to grow on media containing glycerol or ethanol as a sole carbon source only in the presence of the drug. Chloramphenicol has a differential effect on protein synthesis in mitochondria of the parent strain and the mutant. Since chloramphenicol is a ribosome-targeting antibiotic we suggest that the differential effect of the drug on parent and mutant mitochondrial protein synthesis is due to the altered properties of mito-ribosomes of the mutant compared to those of the parent strain. Mitochondria of the mutant synthesize all the mitochondrially encoded polypeptides, however, in significantly lowered amounts. A suggestion is put forward for the existence of a common component (a ribosomal protein) for mito and cyto-ribosomes.
