AHAS is an essential enzyme for many organisms as it catalyzes the
first step in the biosynthesis of the branched-chain amino acids
valine, isoleucine, and leucine.
A common mutant form of the ahas gene was isolated from a
herbicide-resistant Arabidopsis thaliana which differs from the
wild type gene by only a single base pair. A "G" to "A" point
mutation results in a single amino acid substitution in which the
serine residue at position 653 is replaced by asparagine
(S653N)
Tests using the mutant isoform of the ahas gene showed that it
confers tolerance to sulfonylurea herbicides in plants. The ahas
mutant isoform may, therefore, be used as a selectable marker in
transgenic plants.
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