Abstract
In addition to the ABC nitrate-nitrite transporter (NrtABCD), Synechococcus elongatus possesses a SulP family permease (LntT) having latent nitrate transport activity. We previously showed that LntT is activated when LntA, a response regulator, is phosphorylated by LntB, a hybrid histidine kinase. Downstream of the lntAB genes is the lntC gene, encoding a hybrid histidine kinase with no autophosphorylation domain. LntC was found to receive the phosphoryl group from LntA in vitro, and was shown to be essential for activation of LntT in vivo. LntC has a C-terminal region of unique amino acid sequence. Expression in S. elongatus cells of a translational fusion of the C-terminal domain of LntC to glutathione S transferase, which mediates dimer formation, led to activation of LntT. These results suggested that dimerization of LntC, which is promoted by phosphorylation of the protein by LntB via LntA, activates LntT in vivo.
