Involvement of the C-Terminal Extension of the α Polypeptide and of the PucC Protein in LH2 Complex Biosynthesis inRubrivivax gelatinosus

Abstract

The facultative phototrophic nonsulfur bacterium Rubrivivax gelatinosus exhibits several differences from other species of purple bacteria in the organization of its photosynthetic genes. In particular, the puc operon contains only the pucB and pucA genes encoding the ␤ and ␣ polypeptides of the light-harvesting 2 (LH2) complex. Downstream of the pucBA operon is the pucC gene in the opposite transcriptional orientation. The transcription of pucBA and pucC has been studied. No pucC transcript was detected either by Northern blotting or by reverse transcription-PCR analysis. The initiation site of pucBA transcription was determined by primer extension, and Northern blot analysis revealed the presence of two transcripts of 0.8 and 0.65 kb. The half-lives of both transcripts are longer in cells grown semiaerobically than in photosynthetically grown cells, and the small transcript is the less stable. It was reported that the ␣ polypeptide, encoded by the pucA gene, presents a C-terminal extension which is not essential for LH2 function in vitro. The biological role of this alanine-and proline-rich C-terminal extension in vivo has been investigated. Two mutants with C-terminal deletions of 13 and 18 residues have been constructed. Both present the two pucBA transcripts, while their phenotypes are, respectively, LH2؉ and LH2 ؊ , suggesting that a minimal length of the C-terminal extension is required for LH2 biogenesis. Another important factor involved in the LH2 biogenesis is the PucC protein. To gain insight into the function of this protein in R. gelatinosus, we constructed and characterized a PucC mutant. The mutant is devoid of LH2 complex under semiaerobiosis but still produces a small amount of these antennae under photosynthetic growth conditions. This conditional phenotype suggests the involvement of another factor in LH2 biogenesis.Rubrivivax gelatinosus is a facultative phototrophic nonsulfur bacterium belonging to the ␤ subclass of Proteobacteria. Most of the photosynthetic genes are grouped in the photosynthetic cluster on the genome. Differences between the gene organization of the R. gelatinosus photosynthetic cluster and those of the ␣ subclass have been reported (13,25,32).Absorption of light and its conversion into chemical energy is performed, in general, by three highly organized transmembrane pigment-protein complexes: two light-harvesting (LH) complexes (LH1 and LH2) and the reaction center (RC) they surround. The light energy is initially trapped by the peripheral antenna LH2 complexes and transferred to LH1 complexes that are closely associated with the RC. The subsequent photon-induced charge separation in the RC initiates a cyclic electron transport and the formation of an electrochemical proton gradient across the membrane that requires the cytochrome bc 1 complex. The antenna complexes show distinct absorption spectra in the infrared, with maxima near 875 nm for LH1 and 800 and 850 nm for LH2 (12).Antenna complexes have been isolated from various species of purple bacteria. The three-dimens...

Regulation of Photosynthesis Genes in Rubrivivax gelatinosus : Transcription Factor PpsR Is Involved in both Negative and Positive Control

“…The transcript of 0.65 kb presents a short half-life (6 min), while the transcript of 0.8 kb presents a half-life of 22.5 Ϯ 3 min. The results were similar to those obtained for the wild type (6 and 25 Ϯ 3 min), indicating that the stability of pucBA mRNA was not affected in the PPSRK mutant (29).…”

“…8). Both transcripts initiate at the same promoter identified by primer extension but end at two distinct terminator structures (29).…”

“…The decrease in LH2 in the PPSRK mutant under semiaerobic conditions could also be a consequence of a reduced stability of the pucBA transcripts in this mutant. The half-lives of the pucBA transcripts have been determined in the wild type (29). For the evaluation of pucBA mRNA decay kinetics, the Northern blot was normalized to rRNA.…”

‘Candidatus Thermochlorobacter aerophilum:’ an aerobic chlorophotoheterotrophic member of the phylum Chlorobi defined by metagenomics and metatranscriptomics

“…switch from oxygenic photosynthesis to respiration and then fermentation (Nold and Ward, 1996, Steunou et al, 2006, Jensen et al, 2011. Other genes in the 'night pattern' cluster included csmC, encoding another GSB-specific chlorosome envelope protein ; pucC, whose product has various roles in photosynthesis (Tichy et al, 1991;Steunou et al, 2004;Jaschke et al, 2008); and genes neighboring csmA and csmC, whose probable functioning in photosynthesis is suggested by these and other data (Cao et al, 2012;Garcia Costas et al, 2012;Supplementary Figure 2). Assuming that translation continues in 'Ca.…”

Control of Peripheral Light-Harvesting Complex Synthesis by a Bacteriophytochrome in the Aerobic Photosynthetic Bacterium Bradyrhizobium Strain BTAi1

“…Such extension has already been observed for the PucA product of several other photosynthetic bacteria. The pucA gene product of Rubrivivax gelatinosus possesses a short alanine-and proline-rich extension, which can be partially reduced without affecting the assembly of the complex (26). On the other hand, the puc2A gene product found in Rhodobacter sphaeroides, which presents a long extension of 209 amino acids, is not functional (35).…”