Figure 1.

ArcA phosphorylation by His₆-ArcB^78–778 and by combinations of His₆-ArcB^78–778 phosphorelay mutants. Purified ArcA was incubated in a 30-μl reaction mixture with [γ-³²P]ATP and His₆-H1-D1-H2 (A), His₆-H1*D1-H2 and His₆-H1-D1*-H2 (B), or His₆-H1*-D1*-H2 and His₆-H1-D1-H2* (C). At the indicated time intervals, 5-μl samples were withdrawn and subjected to SDS-PAGE analysis. Coomassie Blue-stained gels revealing protein bands (top panels), corresponding autoradiograms (middle panels), and schemes showing the permitted ∼P transfers into ArcB dimers (bottom panels) are presented. The molecular mass standard values (kDa) are shown on the left, and the position of each polypeptide in the gel is indicated on the right of each panel. D, relative amount of ArcA-P formed, as quantified by densitometric analysis of the autoradiogams. Data represent the averages from at least three independent experiments, and S.D. values (error bars) are indicated.