A dual role for the Bacillus subtilis glpD leader and the GlpP protein in the regulated expression of glpD: antitermination and control of mRNA stability

The Bacillus subtilis glpD gene encodes glycerol-3-phosphate dehydrogenase. This gene is preceded by a leader region containing an inverted repeat which acts as a transcription terminator. Expression of glpD is controlled by antitermination of transcription at the inverted repeat. Antitermination is effected by the glpP gene product in conjunction with glycerol-3-phosphate and, consequently, GlpP mutants fail to grow on glycerol as a sole carbon and energy source. We have isolated a number of glycerol-positive revertants of GlpP mutants. Most of these revertants have mutations in the inverted repeat of the glpD leader and produce glycerol-3-phosphate dehydrogenase constitutively. Unlike wild-type bacteria, they are not sensitive to glucose repression of glpD. A few of the revertants are temperature sensitive, i.e. they grow on glycerol at 32°C but not at 45°C and produce glycerol-3-phosphate dehydrogenase only at 32°C. Northern blot analyses demonstrated that the temperature-sensitive expression of glpD is due to destabilization of glpD mRNA. Furthermore, introduction of the wild-type glpP gene into the revertants stabilized the glpD mRNA. This is probably a result of a direct interaction between the GlpP protein and the leader of glpD mRNA. Besides its function in antitermination of transcription of glpD, it is suggested that GlpP is also involved in controlling glpD mRNA stability. Introduction of the glpP gene into the revertants also restored glucose repression, indicating that this repression is mediated by the GlpP protein.