title: Suppression of temperature-sensitive defects of polypeptide release factors RF-1 and RF-2 by mutations or by an excess of RF-3 in Escherichia coli.
abstract: The termination of protein synthesis in bacteria requires two codon-specific polypeptide-release factors, RF-1 and RF-2. A third factor, RF-3, stimulates the RF-1 and RF-2 activities in vitro. To clarify the in vivo role of RF-3 for the RF-2 dependent termination, we isolated and characterized suppressor mutations for the temperature-sensitive RF-2 mutation prfB286. One of the intergenic suppressor mutations, srb-1, acquired an up-promoter alteration in the RF-3 gene, which enhanced the RF-3 expression four- to fivefold. Consistently a threefold increase in the RF-3 level by a promoter-controlled expression plasmid suppressed prfB286. On the other hand, a temperature-sensitive mutation in RF-1, prfA1, was suppressed only slightly by the high-level expression of wild-type RF-3. The RF-3 mutations that suppress prfA1 were isolated and named sra. They were classified into four specific alleles; two each in the N and C-terminal regions. These altered RF-3 proteins restored the RF-1-dependent termination at UAG in prfA1 cells. Moreover, they enhanced the RF-2-dependent UGA termination in both wild-type and prfB286 cells. The termination-stimulating activity of RF-3 was further additively increased by the double sra mutations, suggesting that they affected two distinct protein domains that modulate the termination reaction. Taking these and other results into consideration, RF-3 is likely to interact functionally and cooperatively with the release factors RF-1 and RF-2 in Escherichia coli.
authors.affiliation: Department of Tumor Biology, University of Tokyo, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Matsumura
authors.forename: K
authors.initials: K
authors.lastname: Ito
authors.forename: Y
authors.initials: Y
authors.lastname: Kawazu
authors.forename: O
authors.initials: O
authors.lastname: Mikuni
authors.forename: Y
authors.initials: Y
authors.lastname: Nakamura
mesh_terms: D001483:Base Sequence; D018388:Codon, Terminator; D004926:Escherichia coli / Q000235:genetics*; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D009154:Mutation; D010443:Peptide Chain Termination, Translational / Q000235:genetics*; D010454:Peptide Termination Factors / Q000235:genetics* / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011994:Recombinant Proteins / Q000378:metabolism; D013489:Suppression, Genetic; D013696:Temperature
chemical_list: D018388:Codon, Terminator; D010454:Peptide Termination Factors; D011994:Recombinant Proteins; C041460:peptide chain termination release factor 2; C087971:peptide-chain-release factor 3