A proposed link between nitrogen and carbon metabolism involving protein phosphorylation in bacteria

We demonstrate that certain phosphoryl transfer proteins of the bacterial phosphotransferase system (PTS), the fructose‐ and mannitol‐specific IIA proteins or domains, are homologous to a class of proteins, one of which is known to affect transcription of some of the nitrogen‐regulatory σ54‐dependent operons in Klebsiella pneumoniae. The phosphorylatable histidyl residue in the homologous PTS proteins and the consensus sequence in the vicinity of the active‐site histidine are fully conserved in all members that comprise this family of proteins. A phylogenetic tree of the eight protein members of this family was constructed, and a “signature” sequence that can serve for the identification of new protein members of this family is proposed. These observations suggest that PTS‐catalyzed protein phosphorylation may provide a regulatory link between carbon and nitrogen assimilation in bacteria.