PROMOTER ACTIVITIES IN VIBRIO-CHOLERAE CTX-PHI PROPHAGE

Comparison of cholera toxin (CT) production directed by different gene constructs and S1 nuclease mapping revealed the presence of a ctxB-sp ecific promoter within the ctxA coding sequence. Initiation of transcr iption in this region occurred in wild-type El Tor and classical bioty pe choleragenic vibrios. We propose that transcription from the ctxB-s pecific promoter and a stronger ribosomal binding site on the ctxB mRN A synergistically contribute to achieve the correct (5B:1A) subunit st oichiometry. Plasmid pB, a CT promoterless vector expressing only CTB, was used to detect promoter activity by restoration of A-subunit synt hesis. Promoter activity expressed in vitro and in vivo was detected u pstream of the zonula occludens toxin gene, suggesting that this facto r could be produced in vivo to contribute to fluid accumulation. No pr omoter activity was detected in vitro and in vivo upstream from the ac cessory cholera enterotoxin gene.