Primary structure and transcription of genes encoding B870 and photosynthetic reaction center apoproteins from Rubrivivax gelatinosus.

Abstract

We determined the nucleotide sequence of the puf operon of Rubrivivax gelatinosus (formerly called Rhodocyclus gelatinosus), a photosynthetic bacterium belonging to the beta subclass of purple bacteria (proteobacteria). The operon contains two unknown open reading frames (ORFs) in addition to five photosynthetic genes which have been reported in species belonging to the alpha subclass. These genes include pufB, -A, -L, -M, and -C coding for the beta and alpha subunits of the B870 light-harvesting protein and for the L, M, and cytochrome subunits of the reaction center complex, respectively. One (ORF1) of the two unknown ORFs locates immediately upstream of pufB, while the other (ORF2) locates between pufB and pufA. The deduced product of ORF1 is a small basic protein composed of 41 amino acids that did not show homology with any other proteins reported to date. The deduced product of ORF2 was composed of 74 amino acids having a hydrophobic region able to span the membrane and showed homology with the beta subunit of B870. The deduced amino acid sequence of the cytochrome subunit of the reaction center of R. gelatinosus had significant deletions in the possible attachment site to the M subunit compared with that of Rhodopseudomonas viridis. This is consistent with the facilitated dissociation of this subunit observed with detergent treatment in R. gelatinosus. Analysis of RNA from R. gelatinosus showed that the puf operon of this bacterium has two transcripts; the major one is 1 kilobase in length and the minor one is 4 kilobase in length. These two transcripts have the same 5'-end, and their stoichiometry appeared to be controlled by a putative hairpin structure between pufA and pufL.