Directed mutational analysis of bacteriochlorophyll a biosynthesis in Rhodobacter capsulatus.
Previous studies have established that most if not all of the genes required for synthesis of the Rhodobacter capsulatus essential photosystem are clustered on a 46 kb region of the chromosome known as the photosynthesis gene cluster. This region has recently been sequenced in its entirety by Hearst and co-workers, revealing the existence of 23 open reading frames, many of which are thought to be involved in the synthesis of bacteriochlorophyll. In this study we have undertaken a systematic directed mutational analysis of 12 open reading frames in the photosynthesis gene cluster to evaluate whether individual open reading frames have a role in photopigment biosynthesis. The results of this analysis demonstrate that mutations constructed in seven open reading frames resulted in a loss of bacteriochlorophyll biosynthesis, concomitant with the accumulation of specific intermediates in the Mg-tetrapyrrole biosynthetic pathway. One mutation was observed to result in partial disruption of bacteriochlorophyll biosynthesis, leading to the accumulation of bacteriochlorophyll as well as an intermediate in the biosynthetic pathway. We also observed that disruptions constructed in four open reading frames had no discernible effect on the synthesis of photopigments. The results of this analysis are discussed with regard to our current understanding of the role of each of these open reading frames in the synthesis of the R. capsulatus photosystem.
Bollivar
D W
DW
Department of Biology, Indiana University Bloomington 47405.
Suzuki
J Y
JY
Beatty
J T
JT
Dobrowolski
J M
JM
Bauer
C E
CE
D001426:Bacterial Proteins / Q000032:analysis / Q000096:biosynthesis* / Q000235:genetics*; D002851:Chromatography, High Pressure Liquid; D004252:DNA Mutational Analysis; D005798:Genes, Bacterial; D045342:Light-Harvesting Protein Complexes; D008969:Molecular Sequence Data; D005810:Multigene Family; D016254:Mutagenesis, Insertional; D016366:Open Reading Frames / Q000235:genetics; D045322:Photosynthetic Reaction Center Complex Proteins / Q000235:genetics*; D010860:Pigments, Biological / Q000032:analysis; D011758:Pyrroles / Q000032:analysis; D016354:Rhodobacter capsulatus / Q000235:genetics / Q000378:metabolism*; D045725:Tetrapyrroles
D001426:Bacterial Proteins; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D010860:Pigments, Biological; D011758:Pyrroles; D045725:Tetrapyrroles; C026083:bacteriochlorophyll A proteins, Bacteria