Expression of a 4 kb segment of the bacteriocinogenic plasmid, pIP404, from Clostridium perfringens is inducible by UV-irradiation. DNA sequence analysis revealed that this region contains three genes: uviA, uviB and bcn encoding the bacteriocin BCN5. Biochemical studies with mRNAs showed that expression was controlled at the transcriptional level and that the genes were organized in two independent transcriptional units, uviAB and bcn, both directed by tandem promoters inducible by UV light. The bcn gene is transcribed from three promoters (P1, P2, P3) while transcription of uviAB is directed by two promoters (P4, P5). With the exception of P4, which bears some resemblance to the consensus eubacterial promoter sequence, none of these promoters was recognized in vitro by the major forms of RNA polymerase from C. perfringens, Bacillus subtilis or Escherichia coli. Promoters P1, P3 and P5, which show striking homology with each other, contain unusual sequences in the '-35' and '-10' regions known to be recognized by RNA polymerase and this might indicate positive control.