Abstract
E. coli B cells infected with T3 phage contain a modified host RNA polymerase in addition to the normal RNA polymerase found in uninfected cells. The modified RNA polymerase behaves differently in its elution properties from the normal enzyme on DEAE-cellulose, phosphocellulose, and DNA-cellulose column chromatography. The modified enzyme also differs from the normal polymerase in some of its enzymatic parameters. The specific activity of the modified RNA polymerase is markedly lower (i.e., (1/4)) than that of the normal enzyme. The decrease in activity is probably due to an alteration in the beta' subunit of the polymerase. A similar modification is also observed in nonpermissive cells infected with a gene-l amber mutant incapable of producing active T3 specific polymerase. An analogous modification in host RNA polymerase does not seem to occur in E. coli cells infected with T7 phage.