Symmetrical transcription in bacteriophage phi 29 DNA.

Transcription of some early genes occurring during phi 29 infection in the absence but not in the presence of chloramphenicol has been shown to depend upon the synthesis of the viral protein p4, the positive regulator of late transcription. In addition, the early promoter B1, responsible for early transcription on the late region of the phi 29 genome, has been accurately mapped by nuclease S1 protection experiments. The deduced promoter sequence shares homology with that of the other early phi 29 promoters previously described and with the consensus sequence of the promoters recognized by the Bacillus subtilis sigma 43-RNA polymerase.