PHOSPHOPROTEIN P-II FROM CYANOBACTERIA - ANALYSIS OF FUNCTIONAL CONSERVATION WITH THE P-II SIGNAL-TRANSDUCTION PROTEIN FROM ESCHERICHIA-COLI

The signal transduction protein P-II from Escherichia coli is modified by uridylylation, whereas its counterpart from the cyanobacterium Syn echococcus PCC 7942 is phosphorylated at a seryl residue. To elucidate functional conservations between these proteins, we compared the Syne chococcus P-II protein with the known properties of the E. coli P-II p rotein. Similar to the E. coli protein, Synechococcus P-II binds the m etabolites 2-oxoglutarate and ATP in a mutually dependent manner. The synergism of ligand binding was analyzed in detail. The ATP-binding si te of Synechococcus P-II could be labelled with 5'-p-fluorosulfonylben zoyladenosine. By heterologous expression of the cyanobacterial glnB g ene in E. coli we showed that Synechococcus P-II can be modified by th e E. coli P-II uridylyltransferase. The presence of Synechococcus P-II prevents signal transduction of E. coli P-II to NtrB, presumably by n on-functional competition. We therefore propose that the-primary funct ion of Synechococcus P-II is to sense 2-oxoglutarate, the carbon skele ton required for nitrogen assimilation.