Sequence of the gene for the large subunit of ribulose 1,5-bisphosphate carboxylase from a gymnosperm, Douglas fir

Abstract

The chloroplast rbcL gene encodes the large subunit ofribulose 1,5-bisphosphate carboxylase [ 3 ], the enzyme that catalyzes CO 2 fixation during photosynthesis [6]. rbcL nucleotide sequences data have been used extensively, and proven to be quite powerful, in studies of plant phylogeny and molecular evolution [9, 10]. Complete sequences have been determined from several monocotyledonous and dicotyledonous angiosperms, algae, photosynthetic bacteria, and a bryophyte [7, 9, 10]. We report here an rbcL gene sequence from a Pinaceous gymnosperm, Douglas fir (Pseudotsuga menziesii (Mirb.) Franco). rbcL was sequenced by the dideoxynucleotide chain termination method using recombinant plasmid DNA as the template [2]. In addition to the 1425 base pair (bp) coding region, we sequenced 251 bp upstream and 179bp downstream of the open reading frame (Fig. 1). The coding region has an inferred amino acid sequence that is 93.0% similar to tobacco [4], 90.3% to maize [5, 8], and 92 .4~ to liverwort [7]; its DNA sequence is 85.8%, 83.8%, and 82.6 % similar, respectively. There is a deletion of one codon and an insertion of one codon in the Douglas fir sequence relative to maize, and a deletion of two codons relative to tobacco. The 5' flanking region contains prokaryoticlike consensus promoter sequences and ribosome binding site. Possible 35 (TTGCAT) and 10 (TACAAT) regions are located at positions 80 to 85 and 103 to 108, respectively (underlined in Fig. 1) and are separated by a 17 bp AT-rich region. The Douglas fir rbcL 35 sequence differs in two nucleotide positions from angiosperm sequences (TTGCAT instead of TTGCGC) [4, 10]. The putative ribosome binding site [1] is also underlined, and located at nucleotides 242 to 246. Two likely stem-loop transcription termination structures [ 10] are present in the 3' flanking region (horizontal arrows in Fig. 1).