Two amino-acid biosynthetic genes are encoded on the plastid genome of the red alga Porphyra umbilicalis.
To isolate the gene encoding the amino-acid biosynthetic enzyme acetolactate synthase (ALS) from the red alga Porphyra umbilicalis, PCR experiments were carried out using P. umbilicalis DNA as the template and degenerate oligonucleotides representing conserved regions of ALS amino-acid sequences. Interestingly, the PCR product (0.9 kb) hybridized exclusively to the plastid DNA of this red alga. DNA sequencing of two contiguous EcoRI plastid DNA clones revealed a 590 amino-acid open reading frame with 55 to 61% identity to cyanobacterial ALS sequences. A second gene (argB) encoding another amino-acid biosynthetic enzyme, N-acetylglutamate kinase, was identified upstream of, and on the opposite strand to the gene encoding ALS (ilvB). This is the first molecular characterization of a gene for an arginine biosynthetic enzyme from any plant. In addition, two tRNA genes, trnT(GGU) and trnY(GUA), were detected downstream from ilvB while four tRNA genes, trnfM(CAU), trnA(GGC), trnA(GGC), trnS(-GCU) and trnD(GUC), were found downstream from argB. trnA(GGC) is not found in the chloroplast genomes of land plants.
National Research Council of Canada, Institute for Marine Biosciences, Halifax, Nova Scotia.
M
M
Reith
J
J
Munholland
D000095:Acetolactate Synthase / Q000235:genetics; D000595:Amino Acid Sequence; D000596:Amino Acids / Q000096:biosynthesis / Q000235:genetics*; D001120:Arginine / Q000235:genetics; D001483:Base Sequence; D004247:DNA; D016678:Genome; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D015388:Organelles / Q000378:metabolism*; D010770:Phosphotransferases / Q000235:genetics; D017851:Phosphotransferases (Carboxyl Group Acceptor); D012343:RNA, Transfer / Q000737:chemistry / Q000235:genetics; D000461:Rhodophyta / Q000235:genetics* / Q000378:metabolism; D016415:Sequence Alignment
D000596:Amino Acids; D004247:DNA; D012343:RNA, Transfer; D001120:Arginine; D000095:Acetolactate Synthase; D010770:Phosphotransferases; D017851:Phosphotransferases (Carboxyl Group Acceptor); C018721:acetylglutamate kinase