GcvA interacts with both the α and σ subunits of RNA polymerase to activate the Escherichia coli gcvB gene and the gcvTHP operon

The glycine cleavage enzyme system in Escherichia coli provides one-carbon units for cellular methylation reactions. The gcvB gene encodes two small RNAs that in turn regulate other genes. The GcvA protein is required for expression of both the gcvTHP (PgcvT) and gcvB (PgcvB) promoters. However, the architectures of the two promoters are different, with the PgcvT promoter representing a class III activator-dependent promoter and the PgcvB promoter representing a class II activator-dependent promoter. The RNA polymerase holoenzyme was examined for its role in transcription activation of the gcvTHP operon and the gcvB gene by the GcvA protein. The results suggest that GcvA interacts with the RNA polymerase α subunit for activation of the gcvTHP operon and interacts with the RNA polymerase σ subunit for activation of the gcvB gene.