This invention provides a DNA sequence capable of encoding an enzyme protein which is the α-subunit of the first isozyme of rice anthranilate synthase (ASA); and a DNA capable of encoding an enzyme protein which is the α-subunit of the second isozyme of 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.
This invention also provides a DNA having a promoter activity for the rice ASA gene, which DNA can be used as a promoter for introducing a useful exogenous gene into rice or other plants and expressing the gene therein.