ThepufQ gene product ofRhodobacter capsulatus is essential for formation of B800-850 light-harvesting complexes

Forrest, M E; Zucconi, Anthony P.; Beatty, J. Thomas

doi:10.1007/bf01570579

Cited by 15 publications

(13 citation statements)

References 17 publications

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“…3c; in several experiments the values of the areas under the 800 nm peaks were approximately 65 O/O of the wild-type controls for low-oxygen cultures, and about 37 YO for photosynthetically grown cultures), and the absorption of the 800nm peak seemed to be disproportionately low relative to that at 850 nm. This 800 nm absorption peak is probably associated with the periplasmic side of the complex (Fowler et al, 1992).…”

Section: Discussionmentioning

confidence: 94%

Rhodobacter capsulatus puc operon: promoter location, transcript sizes and effects of deletions on photosynthetic growth

1993

Journal of General Microbiology

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Gene deletions of the puc operon of Rhodobacter capsulatus showed that the pucC and pucE genes, but not pucD, were required for formation of wild-type levels of the LHII complex. Deletion of pucC or pucE also impaired photosynthetic growth. The effects of pucC deletion were suppressed by secondary mutations that mapped outside the puc operon. Fusion of a Zac'Z gene to PUCE' showed that most of pucE transcription originated from upstream of pucB. RNA blot analysis revealed a 2.4 kb transcript that hybridized to probes specific for the pucBA, pucC and pucDE regions, indicating that some puc operon messages extend from just before the pucB gene to just after the PUCE gene.

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Section: Discussionmentioning

confidence: 94%

Rhodobacter capsulatus puc operon: promoter location, transcript sizes and effects of deletions on photosynthetic growth

1993

Journal of General Microbiology

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“…This change was made to facilitate mapping of the suppressor mutations and does not alter the phenotype from that observed for ⌬RC6(pTL2). Plasmid p⌬4 contains the puf operon promoter and the pufQ gene (1), expression of which is necessary for optimal formation of the B800-850 complex in ⌬RC6 (9).…”

Section: Methodsmentioning

confidence: 99%

Mutation of the Ser2 codon of the light-harvesting B870 alpha polypeptide of Rhodobacter capsulatus partially suppresses the pufX phenotype

1995

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The exact function of the pufX gene product of Rhodobacter capsulatus is uncertain, but deletion of the pufX gene renders cells incapable of phototrophic growth on a minimal medium, and photosynthetic electron transfer is impaired in vitro. However, suppressor mutants that are able to grow phototropically are readily isolated. Two such suppressor mutants were characterized as to their phototrophic growth properties, their fluorescence at different incident light intensities, the integrity of their chromatophores, and their abilities to generate a transmembrane potential. We found that the photosynthetic apparatus in the suppressor mutants was less stable than that of the pseudo-wild-type and primary mutant strains and that the suppressor mutants used light energy less efficiently than the pseudo-wild-type strain. Therefore, the suppressor strains are more precisely designated partial suppressor mutants. The locations and sequences of the suppressor mutations were determined, and both were found to change the second codon of the pufA gene. It is hypothesized that the serine residue specified by this codon is important in interactions between the B870 ␣ protein and other membrane-bound polypeptides and that suppressor mutations at this position partially compensate for loss of the PufX protein. A model is proposed for the function of the PufX protein.The purple nonsulfur bacterium Rhodobacter capsulatus is capable of both respiratory and phototrophic growth under appropriate conditions. Since the photosynthetic apparatus can be gratuitously induced during aerobic dark growth simply by lowering the oxygen concentration, R. capsulatus is a good model organism for mutational studies of the assembly and function of photosynthetic membrane-bound electron transport complexes.Energy capture during phototrophic growth is accomplished by what is herein designated the photosynthetic unit. The photosynthetic unit of R. capsulatus is composed of three types of integral membrane polypeptide complexes: the light-harvesting antennae (although several designations have been given for light-harvesting complexes in different species of purple bacteria, in this report we use B800-850 for LH2 and B870 for LH1 complexes); the reaction center, which mediates the formation of a transmembrane potential by using the energy captured by the antenna complexes; and the ubiquinol:cytochrome b-c 1 complex (b-c 1 complex), which converts the transmembrane potential to a proton gradient. A variety of experimental and theoretical data are consistent with the view that in wildtype cells of purple nonsulfur bacteria, these three types of complexes are organized in the membrane in such a way as to enhance functional interactions with each other (16,34). A structural interaction between the R. capsulatus reaction center and B870 antenna complex was indicated by the finding that a single amino acid change of the B870 ␣ polypeptide caused the loss of the B870 complex and resulted in a change in the position of the reaction center. Consequently, the reac...

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“…The search for elements involved in the regulation of Bchl biosynthesis caused attention to be focused on the pufQ open reading frame located at the extreme 5' end of thepuf operon in both R. capsulatus (1,3,4,17,23) and R. sphaeroides (15,22 ThepufQ gene was then altered by site-directed mutagenesis to produce a sequence, 5' of the coding region, which is a consensus ribosome-binding site (RBS) of genes that are well expressed in E. coli (36). An XbaI restriction site was also introduced at the extreme 5' end of the initiation codon to allow facile subcloning of the pufQ gene in the fusion vectors.…”

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confidence: 99%

Recombinant expression of the pufQ gene of Rhodobacter capsulatus

et al. 1993

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Genetic studies have shown that the expression of the pufQ gene is required for normal levels of bacteriochlorophyll biosynthesis in Rhodobacter capsulatus. Yet, the exact function of the puJQ gene is unknown, and a puJQ gene product has never been isolated. We describe the recombinant overexpression of pufQ in Escherichia coli, as well as the purification and characterization of its gene product, the 74-amino-acid PufQ protein. Site-directed of R. capsulatus into operons and superoperons has recently been reviewed (37). The relative positions of the puf and puh operons and many of the bch and crt genes in the closely related bacterium Rhodobacter sphaeroides are similar to those found for the equivalent genes of R capsulatus (14). However, the distance between the puf and puh operons is some 10 kb shorter (40), and the photosynthetic gene cluster extends to include genes encoding other photosynthetic components, including cytochrome c2 (cycA) and the a-and 1-subunits of the B800-850 light-harvesting complex II (pucB and pucA, respectively, in the puc operon) (40).The biosynthesis of Bchl in both R. capsulatus and R.

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ThepufQ gene product ofRhodobacter capsulatus is essential for formation of B800-850 light-harvesting complexes

Cited by 15 publications

References 17 publications

Rhodobacter capsulatus puc operon: promoter location, transcript sizes and effects of deletions on photosynthetic growth

Rhodobacter capsulatus puc operon: promoter location, transcript sizes and effects of deletions on photosynthetic growth

Mutation of the Ser2 codon of the light-harvesting B870 alpha polypeptide of Rhodobacter capsulatus partially suppresses the pufX phenotype

Recombinant expression of the pufQ gene of Rhodobacter capsulatus

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