ABSTRACT
A temperature-sensitive lethal mutant of Escherichia coli has been constructed by combining two temperature-insensitive mutations: a rif180 mutation that modifies RNA polymerase (RNA nucleotidyltransferase; nucleosidetriphosphate:RNA nucleotidyltransferase, EC 2.7.7.6) and a strA24 mutation that modifies the ribosomal protein S12. The temperature sensitivity is a property of the combination of these two particular alleles; replacement of either of the alleles relieves the temperature sensitivity. An isogenic strain containing a different strA mutation (i.e., rif180 strA11) is not temperature sensitive. Evidently ribosomes modified by the particular strA24 polymerase altered by the rif180 mutation, which suggests that in vivo there may exist some interaction between structures of ribosomes and the RNA polymerase.
Subject(s)
DNA-Directed RNA Polymerases/metabolism , Mutation , Ribosomes/physiology , Temperature , Bacterial Proteins/biosynthesis , Escherichia coli , Genotype , Phenotype , Ribosomal Proteins/physiology , Rifampin/pharmacology , Streptomycin/pharmacology , Transduction, GeneticABSTRACT
Introduction of str A mutations frequently make "male" strains of Escherichia coli permissive to bacteriophage T7; certain rif mutations reverse the permissive effect of strA mutation. Permissiveness of the strA mutation is accompanied by enhanced transcription of bacteriophage T7 genome. Introduction of the nonpermissive rif allele to the permissive strA strain reduces or abolishes the transcription of T7 genome. Thus, a link is implied in the functioning of the ribosome and the RNA polymerase (RNA nucleotidyltransferase, EC 2.7.7.6).
Subject(s)
Coliphages/metabolism , Drug Resistance, Microbial , Escherichia coli/metabolism , Mutation , Rifampin/pharmacology , Streptomycin/pharmacology , Carbon Radioisotopes , Escherichia coli/drug effects , Escherichia coli/radiation effects , Genetics, Microbial , Isotope Labeling , Kinetics , RNA, Viral/biosynthesis , Radiation Effects , Time Factors , Transcription, Genetic , Ultraviolet Rays , Uracil/metabolismABSTRACT
Several streptomycin-resistant mutants of Escherichia coli have been isolated which require exogenous isoleucine for growth. The majority of these strains were of streptomycin-dependent phenotype. If grown in the absence of streptomycin, these streptomycin-dependent auxotrophs (Sm(d-aux)) strains were unable to produce beta-galactosidase and aldolase activities and also failed to exhibit donor properties in conjugation. Genetic analysis indicated that the isoleucine requirement of these strains could be caused by a mutation at the strA locus.