title: Cloning and sequence analysis of cDNA encoding aspartate aminotransferase isozymes from Panicum miliaceum L., a C4 plant.
abstract: The cytosolic and mitochondrial isozymes of aspartate aminotransferase (AspAT) function in the C4 dicarboxylate cycle of photosynthesis. We constructed a cDNA library from leaf tissues of Panicum miliaceum, an NAD-malic-enzyme-type C4 plant and screened the library for AspAT isozymes. A full-length cDNA clone for cytosolic AspAT was isolated. This clone contains an open reading frame that encodes 409 amino acids. We also isolated two cDNA clones for different precursors of mitochondrial AspAT. Comparing these two sequences in the coding regions, we found 12 amino acid substitutions out of 28 base substitutions. The encoded amino acid sequences predict that mitochondrial AspAT are synthesized as precursor proteins of 428 amino acid residues, which each consist of a mature enzyme of 400 amino acid residues and a 28-amino-acid presequence. This prediction coincides with the observation that the in vitro translation product of the mRNA for mitochondrial AspAT was substantially larger than the mature form. A comparison of the amino acid sequences of the AspAT isozymes from P. miliaceum with the published sequences for the enzymes from various animals and microorganisms reveals that functionally and/or structurally important residues are almost entirely conserved in all AspAT species.
authors.affiliation: Department of Agricultural Chemistry, School of Agriculture, Nagoya University, Chikusa, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Taniguchi
authors.forename: H
authors.initials: H
authors.lastname: Sawaki
authors.forename: H
authors.initials: H
authors.lastname: Sasakawa
authors.forename: T
authors.initials: T
authors.lastname: Hase
authors.forename: T
authors.initials: T
authors.lastname: Sugiyama
mesh_terms: D000595:Amino Acid Sequence; D001219:Aspartate Aminotransferases / Q000235:genetics*; D001483:Base Sequence; D003001:Cloning, Molecular; D004247:DNA / Q000235:genetics*; D004591:Electrophoresis, Polyacrylamide Gel; D007527:Isoenzymes / Q000235:genetics*; D008969:Molecular Sequence Data; D010944:Plants / Q000201:enzymology*; D011233:Precipitin Tests; D014176:Protein Biosynthesis; D015183:Restriction Mapping; D016415:Sequence Alignment; D012689:Sequence Homology, Nucleic Acid
chemical_list: D007527:Isoenzymes; D004247:DNA; D001219:Aspartate Aminotransferases