prrA, a putative response regulator involved in oxygen regulation of photosynthesis gene expression in Rhodobacter sphaeroides

Abstract

A new locus, prrA, involved in the regulation of photosynthesis gene expression in response to oxygen, has been identified in Rhodobacter sphaeroides. Inactivation of prrA results in the absence of photosynthetic spectral complexes. The prrA gene product has strong homology to response regulators associated with signal transduction in other prokaryotes. When prrA is present in multiple copies, cells produce light-harvesting complexes under aerobic growth conditions, suggesting that prrA affects photosynthesis gene expression positively in response to oxygen deprivation. Analysis of the expression of puc::lacZ fusions in wild-type and PrrA- cells revealed a substantial decrease in LacZ expression in the absence of prrA under all conditions of growth, especially when cells were grown anaerobically in the dark in the presence of dimethyl sulfoxide. Northern (RNA) and slot blot hybridizations confirmed the beta-galactoside results for puc and revealed additional positive regulation of puf, puhA, and cycA by PrrA. The effect of truncated PrrA on photosynthesis gene expression in the presence of low oxygen levels can be explained by assuming that PrrA may be effective as a multimer. PrrA was found to act on the downstream regulatory sequences (J. K. Lee and S. Kaplan, J. Bacteriol. 174:1146-1157, 1992) of the puc operon regulatory region. Finally, two spontaneous prrA mutations that abolish prrA function by changing amino acids in the amino-terminal domain of the protein were isolated.