New classes of mutants in complementary chromatic adaptation provide evidence for a novel four-step phosphorelay system

Complementary chromatic adaptation appears to be controlled by a complex regulatory system with similarity to four-step phosphorelays. Such pathways utilize two histidine and two aspartate residues for signal transduction, Previous studies of the signaling system controlling complementary chromatic adaptation have uncovered two elements of this pathway, a putative sensor, RcaE, and a response regulator, RcaC. In this work we describe a second response regulator controlling complementary chromatic adaptation, RcaF, and identify putative DNA binding and histidine phosphoacceptor domains within ReaC. RcaF is a small response regulator with similarity to Spo0F of Bacillus subtillis; the latter functions in the four-step phosphorelay system controlling sporulation. We have also determined that within this phosphorelay pathway, RcaE precedes RcaF, and RcaC is probably downstream of RcaE and RcaF, This signal transduction pathway is novel because it appears to use at least five, instead of foul; phosphoacceptor domains in the phosphorelay circuit.