The serine hydroxymethyltransferase gene glyA in Corynebacterium glutamicum is controlled by GlyR.

Serine hydroxymethyltransferase (SHMT) occupies a central position in one-carbon metabolism, and we here study its regulation in Corynebacterium glutamicum. Enzyme quantifications revealed an about 3-fold increase of SHMT activity during exponential growth with a further increase at the onset of the stationary phase. The SHMT encoding glyA gene was shown to be transcribed as a monocistronic mRNA, and its transcriptional start site was determined. Using DNA affinity chromatography the regulator GlyR (Cg0527) was identified and its chromosomal deletion shown to abolish the increase in SHMT activity in the stationary phase. The involvement of GlyR in glyA control was further confirmed by a transcriptional fusion of the glyA promoter with cat and chloramphenicol acetyltransferase quantifications. GlyR was isolated and mutational studies together with electrophoretic mobility shift assays showed that it binds to the imperfect palindromic motif CACT-N(2)-AATG in the -119 to -96 upstream region of the glyA promoter. These and further data illustrate that the essential SHMT has highest activity in the stationary phase and that GlyR acts as an activator of glyA transcription in this growth phase.