Transcriptional regulation of bialaphos biosynthesis in Streptomyces hygroscopicus

A DNA sequence (brpA) which regulates the expression of the genes of the bialaphos biosynthesis pathway (bap) in Streptomyces hygroscopicus was identified and characterized. A newly isolated nonproducing mutant (NP57) had a pleiotropic defect involving at least 6 of the 13 known bap genes; only the step 6 conversion could be detected. NP57 was more sensitive to bialaphos than its parent and had depressed levels of the demethylphosphinothricin acetyltransferase activity (step 10 in the pathway) which confers bialaphos resistance. Sodium dodecyl sulfate-polyacrylamide gel electrophoretic analysis of extracts of this mutant showed that it lacked proteins corresponding to steps 5 and 10. NP57 lacked mRNAs for steps 5, 10, and 13. Bialaphos productivity of NP57 was restored by transformation with a plasmid containing a 5.9-kilobase DNA fragment which was adjacent to the structural gene cluster. Subcloning experiments showed that a 1.3-kilobase fragment from this primary clone restored all the defects of NP57. We conclude that brpA can activate the transcription of the bialaphos resistance gene as well as at least six other bap structural genes.