Cytochrome c ₂ is not essential for photosynthetic growth of Rhodopseudomonas capsulata

Abstract

The structural gene for cytochrome c 2 ( cycA ) of the photosynthetic bacterium Rhodopseudomonas capsulata has been cloned, and the nucleotide and deduced polypeptide sequences have been determined. Compared with the known amino acid sequence of the purified cytochrome c 2 , the nucleotide sequence corresponding to the N-terminal part of the cycA gene product indicates the presence of a putative 21 amino acid signal sequence. Thus, cytochrome c 2 may be synthesized as a precursor which is processed during its secretion to the periplasm. Insertion and insertion-deletion mutations were constructed in vitro and the chromosomal cycA + allele of a wild-type strain was replaced with these mutations by homologous recombination to yield c 2 - mutants of R. capsulata . The c 2 - mutants are stable, and they can grow by photosynthesis and by respiration. Since cytochrome c 2 is the primary electron donor to the reaction center during photosynthesis, the ability of these mutants to grow photosynthetically indicates that an alternative way(s) of reducing the oxidized reaction center must exist in R. capsulata . One candidate for this role may be the membrane-bound cytochrome c 1 .

Sequence analysis and transcriptional organization of the Rhodopseudomonas viridis cytochrome c2 gene

“…2). As reported for other photosynthetic bacteria (12,16,39), a putative signal sequence was found at the 5' end of the R. viridis cycA gene. This signal peptide contains two basic amino acids close to the amino terminus (N-region), followed by a 17-residue hydrophobic stretch and C-region, thus resembling typical procaryotic signal sequences (43).…”

CcmI Subunit of CcmFHI Heme Ligation Complex Functions as an Apocytochrome c Chaperone during c-Type Cytochrome Maturation

“…R. capsulatus strains were grown chemo-heterotrophically (i.e. by respiration) at 35°C on enriched (mineral-peptone-yeast extract medium) medium supplemented as needed with tetracycline at 2.5 g per ml final concentration (25). E. coli strains were grown aerobically at 37°C in Luria-Bertani (LB) broth medium supplemented with ampicillin at a final concentration of 100 g/ml.…”

“…Membrane Proteins-R. capsulatus MT1131 cells were resuspended in buffer A (50 mM Tris-HCl, pH 8.0, 50 mM NaCl, 5 mM EDTA, 1 mM PMSF) and intracytoplasmic membrane vesicles (chromotophores) prepared using a French pressure cell (25). After a 30-min low speed centrifugation (4°C and 14,000 ϫ g) the supernatant was further centrifuged for 2 h at 4°C and 138,000 ϫ g to pellet chromatophores.…”

Synthesis and Assembly of Mitochondrial Proteins

“…Indeed, the equivalent Fe/S protein from the photosynthetic bacteria Rhodopseudomonas sphaeroides is synthesized in the bacterial cytoplasm (comparable to the mitochondrial matrix) and transferred across the photosynthetic membrane to the side opposite the cytoplasm where, as in mitochondria, it is topologically opposed to the Fj part of ATPase. This transfer is accompanied by a reduction in molecular weight (Gabellini et al, 1985) which may be equivalent to processing of the mitochon- Harnisch et al (1985) (N. crassa Fe/S protein of bcx complex), Gabellini and Sebald (1986) (R. sphaeroides Fe/S protein of bcx complex and cytochrome c,), Sadler et al (1984) (yeast cytochrome c^, Lederer and Simon (1974) (N. crassa cytochrome c), Daldal et al (1986) …”