AN ESCHERICHIA-COLI-B MUTATION, RPOB5081, THAT PREVENTS GROWTH OF PHAGE-T4 STRAINS DEFECTIVE IN HOST DNA-DEGRADATION

An E. coli B Tab strain, EM121, was isolated that restricts T4 denA (D NA endonuclease II) mutants at 37 degrees C and above, but is permissi ve for wild-type T4 at all temperatures examined. At 42 degrees C, oth er mutants affected in nucleic acid metabolism (T4 dexA, regA and uvsW strains) are also restricted, Genetic analysis revealed that one muta tion (rpoB5081) in the RNA polymerase beta subunit gene is sufficient for restricting all denA mutants. rpoB5081, together with a second lin ked mutation, is also required for restricting the other T4 mutants. r poB5081 (P806S), previously shown to increase transcription terminatio n in E. coli K-12, causes delayed synthesis of T4 late proteins and re duced DNA synthesis in denA infections. Thus, T4 DNA synthesis and gen e expression are impaired by the rpoB5081 beta subunit when degradatio n of host DNA is reduced. Because the restricted T4 mutants are not re adily distinguished from wild-type phage under typical plating conditi ons, EM121 is an important host for screening and mapping T4 denA muta tions.