The basal-level expression of the cytochrome P450(BM-1) gene is negativelyaffected by the bm1P1 gene of bacillus megaterium

Evidence against the Bm1P1 protein as a positive transcription factor for b arbiturate-mediated induction of cytochrome P450(BM-1) in Bacillus megateri um has been provided in our previous report. In the present study, we show that the basal-level expression of the P450(BM-1) promoter-xylE transcripti onal fusion is significantly reduced when the bm1P1 gene is present on the same plasmid. Moreover, disruption of the chromosomal bm1P1 gene results in enhanced expression of the P450(BM-1) promoter-xylE fusion on a multicopy plasmid. By using a binary vector system, we found that expression of the P 450BM-1 promoter-xylE fusion from a high-copy plasmid is substantially repr essed by expression of bm1P1 from a low-copy plasmid. Taken together, these results suggest that the basal-level expression of P450(BM-1) is negativel y affected by bm1P1. Possible mechanisms for this control are discussed.