ROLE OF G-FACTOR IN PROTEIN SYNTHESIS . STUDIES ON A TEMPERATURE-SENSITIVE ESCHERICHIA COLI MUTANT WITH AN ALTERED G-FACTOR

A temperature-sensitive Escherichia coli mutant with a specific defect in a supernatant factor required for protein synthesis has been studied. The altered factor has been identified as G by DEAE-Sephadex column chromatography: in a polyuridylic acid-directed cell-free system the addition of wild-type G restores the ability of the mutant supernatant to synthesize polyphenylalanine. When NH4Cl-washed ribosomes and purified T factor from the mutant are incubated in the presence of polyuridylic acid, guanosine triphosphate, and [14C]phenylalanine transfer ribonucleic acid, the binding of aminoacyl transfer ribonucleic acid to ribosomes proceeds normally. Paper chromatography of the products of the binding reaction shows the presence of a dipeptide peak with trace amount of tripeptides. The addition of wild-type G to the binding mixture results in a decrease of the dipeptide peak with parallel increase of tripeptides and longer polypeptide chains. Experiments with puromycin indicate that ribosomes from the mutant are not impaired in their ability to form a peptide bond with the antibiotic. In conclusion washed ribosomes from the mutant are able to synthesize a single peptide bond. Chain elongation depends upon the addition of G factor prepared from wild type. © 1969, American Chemical Society. All rights reserved.