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B6db references: 9620268

type Journal Article
authors Gebhardt, J.S.; Wadsworth, G.J.; Matthews, B.F.
title Characterization of a single soybean cDNA encoding cytosolic and glyoxysomal isozymes of aspartate aminotransferase
journal Plant Mol Biol
sel selected
ui 9620268
year (1998)
volume 37
number 1
pages 99-108
keywords Amino Acid Sequence
abstract A soybean cDNA clone, pSAT1, which encodes both the cytosolic and glyoxysomal isozymes of aspartate aminotransferase (AAT; EC was isolated. Genomic Southern blots and analysis of genomic clones indicated pSAT1 was encoded by a single copy gene. pSAT1 contained an open reading frame with ca. 90% amino acid identity to alfalfa and lupin cytosolic AAT and two in-frame start codons, designated ATG1 and ATG2. Alignment of this protein with other plant cytosolic AAT isozymes revealed a 37 amino acid N-terminal extension with characteristics of a peroxisomal targeting signal, designated PTS2, including the modified consensus sequence RL-X5-HF. The second start codon ATG2 aligned with previously reported start codons for plant cytosolic AAT cDNAs. Plasmids constructed to express the open reading frame initiated by each of the putative start codons produced proteins with AAT activity in Escherichia coli. Immune serum raised against the pSAT1-encoded protein reacted with three soybean AAT isozymes, AAT1 (glyoxysomal), AAT2 (cytosolic), and AAT3 (subcellular location unknown). We propose the glyoxysomal isozyme AAT1 is produced by translational initiation from ATG1 and the cytosolic isozyme AAT2 is produced by translational initiation from ATG2. N-terminal sequencing of purified AAT1 revealed complete identity with the pSAT1-encoded protein and was consistent with the processing of the PTS2. Analysis of cytosolic AAT genomic sequences from several other plant species revealed conservation of the two in-frame start codons and the PTS2 sequence, suggesting that these other species may utilize a single gene to generate both cytosolic and glyoxysomal or peroxisomal forms of AAT.
last changed 2010/11/09 16:03

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