REGULATION OF CAROTENOID AND BACTERIOCHLOROPHYLL BIOSYNTHESIS GENES AND IDENTIFICATION OF AN EVOLUTIONARILY CONSERVED GENE REQUIRED FOR BACTERIOCHLOROPHYLL ACCUMULATION

The temporal expression of ten clustered genes required for carotenoid (crt) and bacteriochlorophyll (bch) biosynthesis was examined during the transition from aerobic respiration to anaerobiosis requisite for the development of the photosynthetic membrane in the bacterium Rhodobacter capsulatus. Accumulation of crtA, crtC, crtD, crtE, crtF, crtK, bchC and bchD mRNAs increased transiently and coordinately, up to 12-fold following removal of oxygen from the growth medium, paralleling increases in mRNAs encoding pigment-binding polypeptides of the photosynthetic apparatus. The crtB and crtI genes, in contrast, were expressed similarly in the presence or absence of oxygen. The regulation patterns of promoters for the crtA and crtI genes and the bchCXYZ operon were characterized using lacZ transcriptional fusion and qualitatively reflected the corresponding mRNA accumulation patterns. We also report that the bchI gene product, encoded by a DNA sequence previously considered to be a portion of crtA, shares 49% sequence identity with the nuclear-encoded Arabidopsis thaliana Cs chloroplast protein required for normal pigmentation in plants.