title: Synthesis and stability of reaction center polypeptides and implications for reaction center assembly in Rhodobacter sphaeroides.
abstract: The synthesis and stability of the H and M polypeptide subunits of the photosynthetic reaction center of Rhodobacter sphaeroides were examined. In wild-type cells, low levels of both M and H were found to be synthesized under aerobic growth conditions, with a 20-fold induction in their synthesis under anaerobic-dark growth conditions. Neither M nor H was stable in aerobic cells, but in anaerobic-dark grown cells stability increased dramatically with the t1/2 going from 4-6 min to values estimated in excess of 4 h. In the H-deficient mutant PUHA1, the synthesis and membrane partitioning of the M subunit were unaffected by the absence of the H subunit but there was a significant decrease in M polypeptide stability in the membranes of PUHA1 relative to wild-type cells. The stability of all or part of the M population in PUHA1 could be restored by providing an H-encoding plasmid in trans. It was also determined that the presence of bacteriochlorophyll in fully aerobic cells had a direct, positive effect on M and H stability, utilizing the oxygen-regulatory mutant strain T1a. Implications for the role of the H subunit and putative assembly factors in reaction center assembly are discussed.
authors.affiliation: Department of Microbiology and Molecular Genetics, University of Texas Health Science Center, Houston 77225.
authors.forename: A R
authors.initials: AR
authors.lastname: Varga
authors.forename: S
authors.initials: S
authors.lastname: Kaplan
mesh_terms: D000332:Aerobiosis; D000693:Anaerobiosis; D003624:Darkness; D007700:Kinetics; D045342:Light-Harvesting Protein Complexes; D046911:Macromolecular Substances; D008715:Methionine / Q000378:metabolism; D008961:Models, Structural; D045322:Photosynthetic Reaction Center Complex Proteins / Q000096:biosynthesis* / Q000737:chemistry / Q000302:isolation & purification; D017433:Protein Structure, Secondary; D012242:Rhodobacter sphaeroides / Q000254:growth & development / Q000378:metabolism*; D013045:Species Specificity; D013462:Sulfur Radioisotopes
chemical_list: D045342:Light-Harvesting Protein Complexes; D046911:Macromolecular Substances; D045322:Photosynthetic Reaction Center Complex Proteins; D013462:Sulfur Radioisotopes; D008715:Methionine