The photosynthesis gene cluster of Rhodobacter sphaeroides

The photosynthetic bacteria are at the forefront of the study of many aspec ts of photosynthesis, including photopigment biosynthesis, photosynthetic-m embrane assembly, light-harvesting, and reaction center photochemistry. The facultative growth of some photosynthetic bacteria, their simple photosyst ems, and their ease of genetic manipulation have all contributed to advance s in these areas. Amongst these bacteria, the purple non-sulfur bacterium R hodobacter sphaeroides has emerged as, arguably, the leading contender for a model system in which to integrate the studies of all the different aspec ts of the assembly and function of the photosynthetic apparatus. Many of th e genes encoding photosynthesis-related proteins are known to be clustered within a small region of the genome in this organism. As a further aid to s tudying the assembly and function of the photosystem of Rb. sphaeroides, th e DNA sequence for a genomic segment containing this photosynthesis gene cl uster (PGC) has been assembled from previous EMBL submissions and formerly unpublished data. The Rb. sphaeroides PGC is 40.7 kb in length and consists of 38 open reading frames encoding the reaction center H, L and M subunits , the alpha and beta polypeptides of the light-harvesting I (B875) complex, and the enzymes of bacteriochlorophyll and carotenoid biosynthesis. PGCs a re a feature of gene organization in several photosynthetic bacteria, and t he similarities between the clusters of Rb. sphaeroides and Rb. capsulatus have been apparent for some time. Here we present the first comprehensive a nalysis of the PGC of Rb. sphaeroides, as well as a comparison with that of Rb. capsulatus.