AdeR, a PucR-Type Transcription Factor, Activates Expression of L-Alanine Dehydrogenase and Is Required for Sporulation of Bacillus subtilis

The Bacillus subtilis ald gene encodes L-alanine dehydrogenase, which catalyzes the NAD(+)-dependent deamination of L-alanine to pyruvate for the generation of energy and is required for normal sporulation. The transcription of ald is induced by alanine, but the mechanism underlying alanine induction remains unknown. Here we report that a gene (formerly yukF and now designated adeR) located upstream of ald is essential for the basal and alanine-inducible expression of ald. The disruption of the adeR gene caused a sporulation defect, whereas the complementation of an adeR mutation with an intact adeR gene restored the sporulation ability. adeR expression was not subject to autoregulation and alanine induction. Deletion and mutation analyses revealed that an inverted repeat, centered at position -74.5 relative to the transcriptional initiation site of ald, was required for ald expression and also likely served as a rho-independent transcription terminator. Electrophoretic mobility shift assays showed that purified His-tagged AdeR was a specific DNA-binding protein and that this inverted repeat was required for AdeR binding. AdeR shows no significant amino acid sequence similarity to the known transcriptional activators of ald genes from other bacteria. AdeR appears to be a member of the PucR family of transcriptional regulators. Its orthologs of unknown function are present in some other Bacillus species. Collectively, these findings support the notion that AdeR is a transcriptional activator which mediates ald expression in response to alanine availability and is important for normal sporulation in B. subtilis.