The gene cluster of constitutes 11 genes (10 are located in the transcriptional order the 11th, , is located upstream and divergently transcribed from these genes) that encode a functional methylamine-oxidizing electron transport branch. The gene encodes a LysR-type transcriptional activator essential for induction of the operon. In this study, the characteristics of that process were established. By using transcriptional fusions integrated into the genome of , it was found that the expression of the gene during growth on methylamine and/or succinate was not autoregulated, but proceeded at a low and constant level. The promoter activity was shown to be controlled by MauR and a second transcriptional regulator. This activity was very high during growth on methylamine, low on succinate plus methylamine, and absent on succinate alone. MauR was overexpressed in by using a T7 RNA polymerase expression system. Gel shift assays indicated that MauR binds to a 403 bp DNA fragment spanning the promoter region. It is concluded from these results that the expression of the structural genes is dependent on MauR and its inducer, methylamine, as well as on another transcription factor. Both activators are required for high-level transcription from the promoter. It is hypothesized that the two activators act synergistically to activate transcription: the effects of the two activators are not additive and either one alone activates the promoter rather weakly.


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