Translation initiation defects in ribosomes from streptomycin dependent strains

Abstract

Summary The possible role of the 30S-localized ribosomal protein S12 in translation initiation processes has been investigated. We have compared the in vitro activities of ribosomes from two streptomycin-dependent mutants bearing genetic lesions at different sites of the S12 structural gene, rpx L. The mutant ribosomes, previously washed free of the in vivo bound streptomycin, can translate poly U but not T4 m RNA. The ribosomes from a mutant with the Sm D phenotype have a partly reduced ability to bind fMethionyl-tRNA under the direction of T4 mRNA but the main defect appears at the stage of fMethionyl-puromycin formation; this defect clearly resides in the mutant 30S subunits. The ribosomes from a mutant with the Drug D phenotype normally catalyse the puromycin transfer reaction. Our results suggest that a certain active conformation of S12 protein plays a critical role in correct initiation of protein synthesis.