Earlier studies showed that RNA polymerase isolated from phage-infected Bacillus subtilis has a different subunit structure than the host polymerase. This modified enzyme transcribes middle and possibly late sequences of DNA in vitro whereas the host polymerase can only synthesize early RNA in vitro. Several modified polymerases containing host core subunits and different complements of phage-specified small polypeptides have now been purified from SP82-infected B. subtilis. The transcriptional specificity of these forms is under investigation. BIBLIOGRAPHIC REFERENCES: Hemphill, H.E. and Whiteley, H.R.: The phages of Bacillus subtilis. Bact. Rev. 39: 257-315, 1975. Lawrie, J.M., Spiegelman, G.B. and Whiteley, H.R.: DNA strand specificity of transcripts produced in vivo and in vitro by RNA polymerase from SP82-infected Bacillus subtilis. J. Virol. 15: 1286-1288, 1975.