title: Inhibition of lacZ gene translation initiation in trp-lac fusion strains.
abstract: Different levels of beta-galactosidase are found in various trp-lac fusion strains. These levels of beta-galactosidase fall within a 60-fold range. The amount of thiogalactoside transacetylase activity detected in these same strains only varies 10-fold and is found in amounts greater than those predicted from the beta-galactosidase levels. The observation that the beta-galactosidase and thiogalactoside transacetylase levels are not directly proportional, that the lacZ messenger ribonucleic acid (mRNA) levels are not proportional to the beta-galactosidase activity, that, at least for the one fusion strain tested, the SuA polarity suppressor does not affect the beta-galactosidase level, and that, in all but one strain, the beta-galactosidase activity appears to reside in normal beta-galactosidase molecules suggests that the disproportionately low production of beta-galactosidase is due to a decrease in the frequency of translation initiation of lacZ mRNA in these strains. Several mechanisms are proposed to explain this decrease. Some possible bases for the disproportional production of beta-galactosidase and thiogalactoside transacetylase are also described. The preferred explanation for these disproportional enzyme levels is that only a fraction of the full complement of ribosomes need initiate translation at lacZ for the functional synthesis of lac mRNA to occur and that once the lac ribonucleic acid is made a full complement of ribosomes can bind at internal translation initiation sites at Y and A.
mesh_terms: D000123:Acetyltransferases / Q000096:biosynthesis / Q000378:metabolism; D001665:Binding Sites; D002874:Chromosome Mapping; D004926:Escherichia coli / Q000201:enzymology / Q000378:metabolism*; D005696:Galactosidases / Q000096:biosynthesis / Q000378:metabolism; D005796:Genes; D006358:Hot Temperature; D007785:Lactose / Q000378:metabolism*; D009154:Mutation; D014176:Protein Biosynthesis; D012329:RNA, Bacterial / Q000096:biosynthesis; D012333:RNA, Messenger / Q000096:biosynthesis; D012270:Ribosomes / Q000378:metabolism; D013865:Thioglycosides; D014364:Tryptophan / Q000096:biosynthesis
chemical_list: D012329:RNA, Bacterial; D012333:RNA, Messenger; D013865:Thioglycosides; D014364:Tryptophan; D000123:Acetyltransferases; D005696:Galactosidases; D007785:Lactose