title: Mutation prlF1 relieves the lethality associated with export of beta-galactosidase hybrid proteins in Escherichia coli.
abstract: The 42-1 lamB-lacZ gene fusion confers a conditionally lethal, export-dependent phenotype known as maltose sensitivity. A maltose-resistant mutant showing decreased beta-galactosidase activity of the hybrid protein, designated prlF1 (protein localization), was unlinked to the lamB-lacZ fusion. This mutation mapped at 70 min on the Escherichia coli linkage map and conferred maltose resistance, a 30-fold reduction in beta-galactosidase activity, and a 30% decrease in cellular growth rate at 30 degrees C that was independent of the presence of a gene fusion. prlF1 also decreased the beta-galactosidase activity and relieved the maltose sensitivity conferred by fusions of lacZ to the gene specifying the periplasmic maltose-binding protein, malE. The decrease in beta-galactosidase activity, however, was specific for exported hybrid proteins. When export of the hybrid protein was blocked by a signal sequence mutation, prlF1 decreased the beta-galactosidase activity only 2.5-fold. Similarly, prlF1 did not affect the beta-galactosidase activity of fusions of lacZ to a gene specifying a nonexported protein, malK.
mesh_terms: D010582:Bacteriophage lambda / Q000235:genetics; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics*; D005696:Galactosidases / Q000235:genetics*; D005796:Genes; D005798:Genes, Bacterial; D005804:Genes, Lethal; D005838:Genotype; D007700:Kinetics; D009154:Mutation; D010641:Phenotype; D013045:Species Specificity; D014158:Transcription, Genetic; D001616:beta-Galactosidase / Q000235:genetics*
chemical_list: D005696:Galactosidases; D001616:beta-Galactosidase