Nucleotide sequences of the continuous and separated petA, petB and petD chloroplast genes in Chlamydomonas reinhardtii

We have mapped and sequenced the petA (cytf), petB (cytb6) and petD (subunit IV) genes on the chloroplast genome of Chlamydomonas reinhardtii. At variance with the pet genes in higher plant chloroplasts, the petB and petD genes are continuous, not adjacent and not located next to the psbB gene. The corresponding polypeptide sequences are highly conserved when compared with their counterparts from other sources but have a few features specific of algal cytb6/f complexes. In particular the transit sequence of cytf displays unique characteristics when compared with those previously described for cytf in higher plants.     

Sequence of the two operons encoding the four core subunits of the cytochrome b(6)f complex from the thermophilic Cyanobacterium synechococcus elongatus

The genes encoding cytochrome f (petA), cytochrome b(6) (petB), the Rieske FeS-protein (petC), and subunit IV (petD) of the cytochrome b(6)f complex from the thermophilic cyanobacterium Synechococcus elongatus were cloned and sequenced. Similar to other cyanobacteria, the structural genes are arranged in two short, single-copy operons, petC/petA and petB/petD, respectively. In addition, five open reading frames with homology to known orfs from the cyanobacterium Synechocystis PCC 6803 were identified in the immediate vicinity of these two operons.     

Localization of the genes coding for the 51 kDa PSII chlorophyll apoprotein,apocytochrome b6, the 65–70 kDa PSI chlorophyll apoproteins and the 44 kDa PSII chlorophyll apoprotein in pea chloroplast DNA

Summary DNA probes isolated from previously mapped spinach genes were used to locate 5 genes on pea ctDNA by heterologous hybridization. The genes mapped include psbC, psaA, psaB, psbB, and petB. PsbB and petB mapped to a 6.7 kbp XbaI DNA fragment adjacent to the petD gene. Northern probes from within the DNA which codes for psbB and petD hybridized to 6 RNAs ranging from 1.2 to 5.6 kbp. The psaA and psaB genes, which code for 65–70 kDa proteins of Photosystem I, were mapped to a 7.5 kbp. XbaI DNA fragment. A 5.8 kbp RNA is transcribed from the region which contains the psaA and psaB genes suggesting that these genes are co-transcribed. Finally the psbC gene which codes for a 44 kDa chlorophyll-protein of Photosystem II was mapped to a 12.3 kbp PstI DNA fragment. The pea psbC open reading frame overlaps the psbD coding sequence and this gene pair is within 3 kbp of the psaA-psaB genes. Overall, the organization of the 3 gene clusters analyzed in peas is similar to that reported for spinach.     

Evolutionary relationships among eubacteria, cyanobacteria, and chloroplasts: evidence from the rpoC1 gene of Anabaena sp. strain PCC 7120.

RNA polymerases of cyanobacteria contain a novel core subunit, gamma, which is absent from the RNA polymerases of other eubacteria. The genes encoding the three largest subunits of RNA polymerase, including gamma, have been isolated from the cyanobacterium Anabaena sp. strain PCC 7120. The genes are linked in the order rpoB, rpoC1, rpoC2 and encode the beta, gamma, and beta' subunits, respectively. These genes are analogous to the rpoBC operon of Escherichia coli, but the functions of rpoC have been split in Anabaena between two genes, rpoC1 and rpoC2. The DNA sequence of the rpoC1 gene was determined and shows that the gamma subunit corresponds to the amino-terminal half of the E. coli beta' subunit. The gamma protein contains several conserved domains found in the largest subunits of all bacterial and eukaryotic RNA polymerases, including a potential zinc finger motif. The spliced rpoC1 gene from spinach chloroplast DNA was expressed in E. coli and shown to encode a protein immunologically related to Anabaena gamma. The similarities in the RNA polymerase gene products and gene organizations between cyanobacteria and chloroplasts support the cyanobacterial origin of chloroplasts and a divergent evolutionary pathway among eubacteria.     

A small family of LLS1-related non-heme oxygenases in plants with an origin amongst oxygenic photosynthesizers

Conservation of Lethal-leaf spot 1 (Lls1) lesion mimic gene in land plants including moss is consistent with its recently reported function as pheophorbide a oxygenase (Pao) which catalyzes a key step in chlorophyll degradation (Pruzinska et al., 2003). A bioinformatics survey of complete plant genomes reveals that LLS1(PAO) belongs to a small 5-member family of non-heme oxygenases defined by the presence of Rieske and mononuclear iron-binding domains. This gene family includes chlorophyll a oxygenase (Cao), choline monooxygenase (Cmo), the gene for a 55 kDa protein associated with protein transport through the inner chloroplast membrane (Tic 55) and a novel 52 kDa protein isolated from chloroplasts (Ptc 52). Analysis of gene structure reveals that these genes diverged prior to monocot/dicot divergence. Homologues of LLS1(PAO), CAO, TIC55 and PTC52 but not CMO are found in the genomes of several cyanobacteria. LLS1(PAO), PTC52, TIC55 and a set of related cyanobacterial homologues share an extended carboxyl terminus containing a novel F/Y/W-x(2)-H-x(3)-C-x(2)-C motif not present in CAO. These proteins appear to have evolved during the transition to oxygenic photosynthesis to play various roles in chlorophyll metabolism. In contrast, CMO homologues are found only in plants and are most closely related to aromatic ring-hydroxylating enzymes from soil-dwelling bacteria, suggesting a more recent evolution of this enzyme, possibly by horizontal gene transfer. Our phylogenetic analysis of 95 extant non-heme dioxygenases provides a useful framework for the classification of LLS1(PAO)-related non-heme oxygenases.