Nucleotide sequence of the genes encoding cytochrome b-559 from the cyanelle genome of Cyanophora paradoxa

Abstract

Cyanophora paradoxa is a flagellated protozoan which possesses unusual, chloroplast-like organelles referred to as cyanelles. The psbE and psbF genes, which encode the two apoprotein subunits of cytochrome b-559, have been cloned from the cyanelle genome of C. paradoxa. The complete nucleotide sequences of these genes and their flanking sequences were determined by the chain-termination, dideoxy method. The psbE gene is composed of 75 codons and predicts a polypeptide of 8462 Da that is seven to nine residues smaller than most other psbE gene products. The psbF gene consists of 43 codons and predicts a polypeptide of 4761 Da. Two open reading frames, whose sequences are highly conserved among cyanobacteria and numerous higher plants, were located in the nucleotide sequence downstream from the psbF gene. The first open reading frame, denoted psbI, is composed of 39 codons, while the second open reading frame, denoted psbJ, is composed of 41 codons. The predicted amino acid sequences of the psbI and psbJ gene products predict proteins of 5473 and 3973 Da respectively. These proteins are probably integral membrane proteins anchored in the membrane by a single, transmembrane alpha helix. The psbEFIJ genes are probably co-transcribed and constitute an operon as found for other organisms. Each of the four genes is preceded by a polypurine sequence which resembles the consensus ribsosome binding sequences for Escherichia coli.

Low‐molecular‐mass proteins in cyanobacterial photosystem II: Identification of psbH and psbK gene products by N‐terminal sequencing

“…Since this gene sequence is present in Synechocystis PCC6803 [21], we can also expect its product in the cyanobacterial PS II core. As shown in fig.1, there are several bands in about the 5 kDa region in the PS II core complex of Synechococcus.…”

A photosystem II polypeptide is encoded by an open reading frame co-transcribed with genes for cytochrome b-559 in wheat chloroplast DNA

“…Just upstream of the ATG translation initiation codon of off40 is a potential ribosome-binding site with sequences complementary to the 3' end of 16S rRNA [30,31,35]. Similar sequences are not obviously present just upstream of orf38 in wheat although ribosome binding sites have been identified just upstream of orf38 in Cyanophora [5] and Euglena [8].…”

“…In Fig. 2 we show the N-terminal amino acid sequence of polypeptides that match amino acid sequences deduced from open reading frames in wheat chlo- [26] and Euglena [8] and the cyanelle genome of Cyanophora [4,5]. This would suggest that the 3.2 kDa polypeptide is synthesised from the wheat gene equivalent to the off38 gene of these organisms.…”

“…5. Comparison of the deduced amino acid sequence of orf38 (A) and orf40 (B) with those from Cyanophora [5], Marchantia [26], Euglena [8] and pea (WiUey and Gray, personal communication). Dashes indicate gaps introduced in the amino acid sequence to obtain maximum alignment.…”

“…These include an open reading frame of 38 amino acids cotranscribed with the psbB and psbH genes and two open reading frames of 38 and 40 codons cotranscribed with the psbE and psbF genes for cytochrome b-559 [13]. The fact that these open reading frames are co-transcribed with known photosystem II polypeptides has led to speculation that they may also encode components of photosystem II [5]. To date, however, no evidence has been published to indicate that polypeptides encoded by these open reading frames are components of photosystem II.…”