Jm. Eraso et S. Kaplan, OXYGEN-INSENSITIVE SYNTHESIS OF THE PHOTOSYNTHETIC MEMBRANES OF RHODOBACTER-SPHAEROIDES - A MUTANT HISTIDINE KINASE, Journal of bacteriology, 177(10), 1995, pp. 2695-2706
Two new loci, prrB and prrC, involved in the positive regulation of ph
otosynthesis gene expression in response to anaerobiosis, have been id
entified in Rhodobacter sphaeroides. prrB encodes a sensor histidine k
inase that is responsive to the removal of oxygen and functions throug
h the response regulator PrrA. Inactivation of prrB results in a subst
antial reduction of photosynthetic spectral complexes as well as in th
e inability of cells to grow photosynthetically at low to medium light
intensities. Together, prrB and prrA provide the major signal involve
d in synthesis of the specialized intracytoplasmic membrane (ICM), har
boring components essential to the light reactions of photosynthesis,
Previously, J. K. Lee and S. Kaplan (J. Bacteriol. 174:1158-1171, 1992
) identified a mutant which resulted in high-level expression of the p
uc operon, encoding the apoproteins giving rise to the B800-850 spectr
al complex, in the presence of oxygen as well as in the synthesis of t
he ICM under conditions of high oxygenation, This mutation is shown to
reside in prrB, resulting in a leucine-to-proline change at position
78 in mutant PrrB (PRRB78), Measurements of mRNA levels in cells conta
ining the prrB78 mutation support the idea that prrB is a global regul
ator of photosynthesis gene expression. Two additional mutants, PRRB1
and PRRB2, which make two truncated forms of the PrrB protein, possess
substantially reduced amounts of spectral complexes. Although the pre
cise role of prrC remains to be determined, evidence suggests that it
too is involved in the regulatory cascade involving prrB and prrA. The
genetic organization of the photosynthesis response regulatory (PRR)
region is discussed.