Transcriptional control of the sulfur-regulated cysH operon, containing genes involved in L-cysteine biosynthesis in Bacillus subtilis.

MARIA CECILIA MANSILLA; ALBANESI, D.; DE-MENDOZA, D.

JOURNAL OF BACTERIOLOGY

AMER SOC MICROBIOLOGY

Año: 2000 vol. 146 p. 815 - 821

0021-9193

The molecular mechanisms of regulation of the genes involved in the biosynthesis of cysteine are poorlycharacterized in Bacillus subtilis and other gram-positive bacteria. In this study we describe the expressionpattern of the B. subtilis cysH operon in response to sulfur starvation. A 6.1-kb polycistronic transcript whichincludes the cysH, cysP, ylnB, ylnC, ylnD, ylnE, and ylnF genes was identified. Its synthesis was induced by sulfurlimitation and strongly repressed by cysteine. The cysH operon contains a 5* leader portion homologous to thatof the S box family of genes involved in sulfur metabolism, which are regulated by a transcription terminationcontrol system. Here we show that induction of B. subtilis cysH operon expression is dependent on the promoterand independent of the leader region terminator, indicating that the operon is regulated at the level oftranscription initiation rather than controlled at the level of premature termination of transcription. Deletionof a 46-bp region adjacent to the 235 region of the cysH promoter led to high-level expression of the operon,even in the presence of cysteine. We also found that O-acetyl-L-serine (OAS), a direct precursor of cysteine,renders cysH transcription independent of sulfur starvation and insensitive to cysteine repression. We proposethat transcription of the cysH operon is negatively regulated by a transcriptional repressor whose activity iscontrolled by the intracellular levels of OAS. Cysteine is predicted to repress transcription by inhibiting thesynthesis of OAS, which would act as an inducer of cysH expression. These novel results provide the first directevidence that cysteine biosynthesis is controlled at a transcriptional level by both negative and positive effectorsin a gram-positive organism.