Nucleotide sequence of the chloroplastpetD gene ofChlamydomonas eugametos

In land plant chloroplast DNAs, the gene coding for subunit IV of the cytochrome b6lf complex (petD) is interrupted by a group II intron and is part of a well-known operon containing also the psbB, psbH and petB genes (1). We have located the chloroplast petD gene of Chlamydomonas eugametos on the 1.4 kbp HindlU subfragment of EcoRl fragment 4 (2) and determined its sequence. In contrast to land plants, this green algal gene is continuous and unlinked to psbB and petB (3). Like its land plant homologues, it encodes a protein of 160 amino acid residues with three potential membrane-spanning regions (underlined) (4). The amino acid sequence derived from the C. eugametos petD gene is 82%, 82% and 83% identical with the corresponding sequences from Marchantia polymorpha (1), tobacco (5) and spinach (6), respectively. No putative -10 and -35 promoter elements were identified upstream of the region corresponding to the 5' terminus of the C. eugametos petD transcript (1.2 kb) as determined by SI nuclease protection (see the region delimited by the bracket) and primer extension (5' termini are indicated by triangles, with their size reflecting RNA abundancy) analyses. Sequences capable of forming stem-loop structures with at least 10 nucleotides in the stem (arrows) were found upstream and downstream of the coding region.