Functional analysis of mlcR, a regulatory gene for ML-236B (compactin) biosynthesis in Penicillium citrinum

The mlcR gene encodes a putative 50.2-kDa protein with a Zn(II)(2)Cys(6) DNA-binding domain, which may be involved in the regulation of ML-236B biosynthesis in Penicillium citrinum. The induction of ML-236B production appears to correlate with the expression of mlcR, and the ML-236B biosynthetic genes mlcA- mlcH, and occurs mostly during the stationary phase. The present study was designed to examine the effects of alterations in mlcR expression on ML-236B biosynthesis. We first set out to increase the mlcR copy number in the chromosome of P. citrinum. Transformants with additional copies of native mlcR showed increased transcription of mlcR and produced larger amounts of ML-236B than the parent strain. Altered mlcR expression was also achieved by introducing a construct, designated pgkA(P)::mlcR, that contained the mlcR coding region fused to the (constitutively active) promoter and terminator sequences of the Aspergillus nidulans 3-phospho-glycerate kinase (pgkA) gene. Transformants carrying the pgkA(P)::mlcR construct expressed mlcR constitutively, and produced ML-236B during the exponential growth phase, suggesting that the pgkA(P)::mlcR construct does affect the regulation of ML-236B biosynthesis. Comparative expression analysis by RT-PCR showed that altering the expression profile of mlcR influenced the expression of some of the ML-236B biosynthetic genes. The evidence suggests that mlcR may indeed be involved in the transcriptional activation of some of the pathway-specific genes required for ML-236B biosynthesis.