A strong promoter of bacteriophage MB78 which controls the expression of a small structural protein of the phage has been identified and characterized. Analysis of its nucloetide sequence upstream of the translational start site revealed the presence of conserved −10 (TAATAT) and −35 (TTCTCCT) regions. It was observed that transcription initiates with thymidine residue, 86 nt upstream of the translational start site. Transcription seems to undergo alternate up and down regulation. This promoter is efficiently recognized by sigma 70 RNA polymerase and a host factor also binds to it. Binding of RNA polymerase is independent of binding of the host factor.