Abstract: A rice anthranilic acid synthase produced by introducing a variation in the base sequence of rice anthranilic acid synthase gene OASA2 so as to effect substitution for specified multiple amino acids. This synthase not only acquires a resistance to feedback inhibition by tryptophan but also retains an enzymatic activity identical with or higher than that of wild type rice anthranilic acid synthase.

Abstract: A DNA sequence is provided, which encodes an enzyme that is the &agr;-subunit of the first isozyme of rice anthranilate synthase (ASA). Transformed plants having a high tryptophan content can be regenerated by culturing the plant cells having introduced therein such a recombinant vector which contains, at a position downstream of a promoter, an inserted DNA fragment carrying the above DNA sequence. In addition, methods of selecting transformed plant cells are disclosed, wherein plant cells transformed with the discloses DNA are resistant to inhibitory concentrations of tryptophan or tryptophan analogues.