Abstract
Synechococcus elongatus possesses a SulP family permease (LtnT) having nitrate transport activity that is regulated by a His-Asp phosphorelay system consisting of LtnA, LtnB, and LtnC. We previously showed that oligomerization of the C-terminal region of LtnC, which is promoted by phosphorylation of the N-terminal HisKA domain of the protein by LtnB via LtnA, activates LtnT. Downstream of the ltnABC genes is the ltnD gene encoding a protein, whose C-terminal region is homologous to the C-terminal region of LtnC. Expression in S. elongatus cells of a translational fusion of the C-terminal region of LtnD to glutathione S-transferase, which mediates dimer formation, also led to activation of LtnT. LtnD was not required for the LtnBAC-dependent activation of LtnT, indicating that LtnD mediates activation of the LtnT permease independently from the His-Asp phosphorelay system.
