Ribonucleic Acid Polymerase Mutant of Escherichia coli Defective in Flagella Formation

AUTOR(ES)
RESUMO

Escherichia coli K-12 mutants that are resistant to bacteriophage χ, defective in motility, and unable to grow at high temperature (42°C) were isolated from among those selected for rifampin resistance at low temperature (30°C) after mutagenesis with N-methyl-N′-nitro-N-nitrosoguanidine. Genetic analysis of one such mutant indicated the presence of two mutations that probably affect the β subunit of ribonucleic acid (RNA) polymerase: one (rif) causing rifampin resistance and the other (Ts-74) conferring resistance to phage χ (and loss of motility) and temperature sensitivity for growth. Observations with an electron microscope revealed that the number of flagella per mutant cell was significantly reduced, suggesting that the Ts-74 mutation somehow affected flagella formation at the permissive temperature. When a mutant culture was transferred from 30 to 42°C, deoxyribonucleic acid synthesis accelerated normally, but RNA or protein synthesis was enhanced relatively little. The rate of synthesis of β and β′ subunits of RNA polymerase was low even at 30°C and was further reduced at 42°C, in contrast to the parental wild-type strain. Expression of the lactose and other sugar fermentation operons, as well as lysogenization with phage λ, occurred normally at 30°C, suggesting that the mutation does not cause general shut-off of gene expression regulated by cyclic adenosine 3′,5′-monophosphate.

ACESSO AO ARTIGO

Documentos Relacionados