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Functional analysis of a gene encoding threonine synthase
from rice
Md. Shafiqul
Islam Sikdar and Jung-Sup Kim*
Faculty
of Biotechnology, Jeju National University, Jeju, 690-756,
Korea.
*Corresponding author. E-mail:
biotech2020@jejunu.ac.kr. Tel: +82-64-754-3393. Fax:
+82-64-754-3393.
Abbreviations: TS,
Threonine synthase; OsTS, Oryza sativa
threonine synthase gene; Thr, threonine; Met,
methionine; Lys, lysine; OPH, O-phosphohomoserine;
cDNA, complementary deoxyribonucleic acid; SAM,
S-adenosylmethionine; CGS, cystathionine-γ-synthase;
EST, expressed sequence tag; PCR, polymerase
chain reaction; ORF, open reading frame; IPTG,
isopropyl β-D-thiogalactopyranoside;
BLAST,
basic local alignment search tool; EMBL, European
molecular biology laboratory.
Accepted
29 January, 2010 |
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Threonine
synthase (TS) is a pyridoxal phosphate dependent enzyme that
catalyzes the formation of threonine (Thr) through O-phosphohomoserine
(OPH) from the aspartate family pathway in plants. The
properties of the TS enzyme have been evaluated in many
bacteria and few plants. Sequence analysis of the cDNA from
rice revealed that it harbors a full-length open reading
frame for OsTS encoding for 521 amino acids,
corresponding to a protein of approximately 57.2 kD. The
predicted amino acid sequence of OsTS is highly
homologous to that of Arabidopsis TS and many
bacterial TS encoded by thrC gene. The OsTS protein
harbors a signature binding motif for pyridoxal- 5’
-phosphate at the amino terminus. A thrC mutant
strain of Escherichia coli was complemented by
OsTS expression. OsTS expression was correlated
with the survival of the thrC mutant, which is
affected by the supplementation of an aspartate pathway
metabolite, methionine.
Key
words:
Oryza sativa, methionine, threonine, threonine
synthase. |
