Research on "E. coli" revealed that GS is regulated through gene expression. The gene that encodes the GS subunit is designated "glnA". Transcription of "glnA" is dependent on "NRI" (a specific transcriptional enhancer). Active transcription occurs if NRI is in its phosphorylated form, designated "NRI-P". Phosphorylation of NRI is catalyzed by NRII, a protein kinase. If NRII is complexed with PIIA then it will function as a phosphatase and NRI-P is converted back to NRI. In this case, transcription of "glnA" ceases.