An E. coli B mutation, rpoB5081, that prevents growth of phage T4 strains defective in host DNA degradation

Abstract

An E. coli B Tab strain, EM121, was isolated that restricts T4 denA (DNA endonuclease II) mutants at 37°C and above, but is permissive for wild-type T4 at all temperatures examined. At 42°C, other mutants affected in nucleic acid metabolism (T4 dexA, regA and uvsW strains) are also restricted. Genetic analysis revealed that one mutation ( rpoB5081) in the RNA polymerase β subunit gene is sufficient for restricting all denA mutants. rpoB5081, together with a second linked mutation, is also required for restricting the other T4 mutants. rpoB5081 (P806S), previously shown to increase transcription termination in E. coli K-12, causes delayed synthesis of T4 late proteins and reduced DNA synthesis in denA infections. Thus, T4 DNA synthesis and gene expression are impaired by the rpoB5081 β subunit when degradation of host DNA is reduced. Because the restricted T4 mutants are not readily distinguished from wild-type phage under typical plating conditions, EM121 is an important host for screening and mapping T4 denA mutations.