The in vivo transcription initiation sites of eight putative phi 29 promoters have been accurately determined: seven of them correspond to early promoters, including the four main ones, and the other corresponds to the only late promoter found in vivo. Comparison of the phi 29 promoter sequences with the consensus sequence for the Bacillus subtilis sigma 43 RNA polymerase suggests that the sigma 43 enzyme is involved in the recognition of the viral early promoters, whereas the late promoter sequences share homology with the consensus sequence only at its -10 region.