Hpr phosphorylation by HprK/P. Hpr-His6 (20 μM) was mixed with HprK/P-His6 (1 μM) in the presence of 2 mM ATP or 20 mM FBP. The reaction products were analyzed by both nondenaturing 12% PAGE and SDS-PAGE. Lane 1, Hpr; lane 2, Hpr and HprK/P; lane 3, Hpr, HprK/P, ATP, and FBP; lane 4, Hpr, HprK/P, and FBP; lane 5, Hpr, HprK/P, and ATP.