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 degrees C and above, but is permissive for wild-type T4 at all temperatures examined. At 42 degrees 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 beta 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 beta 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.