A gene required for the regulation of photosynthetic light harvesting in the cyanobacterium Synechocystis 6803

A gene required for the short-term regulation of photosynthetic light harvesting (the state transition) has been identified in the cyanobacterium Synechocystis sp. PCC6803. The open reading frame is designated sll1926 in the complete Synechocystis gene sequence. The deduced amino acid sequence has no homologues in current sequence databases and no recognizable sequence motifs. It encodes a putative integral membrane protein of 16 kDa, which we have designated RpaC (regulator of phycobilisome association C). Fluorescence measurements of an insertional inactivation mutant of rpaC (Delta sll1926) show that it is specifically unable to perform state transitions. Delta sll1926 has approximately wild-type levels of PS1, PS2 and phycobilisomes. Measurements of oxygen evolution and uptake show Delta sll1926 to have no deficiency in electron transport rates. In vitro [gamma-P-32]-ATP labelling experiments suggest that RpaC is not the 15 kDa membrane phosphoprotein previously implicated in state transitions. Delta sll1926 grows more slowly than the wild type only at very low light intensities.