cDNAs (RISBZ1, RISBZ4, and RISBZ5) encoding bZIP transcription factors were isolated from a cDNA library originating in rice plant seed. The cDNAs encode novel proteins and have binding activity to the GCN4 motif. Among them, RISBZ1 activated transcription mediated by the GCN4 motif by 100-fold or more. Since the expression of RISBZ1 precedes the expression of a seed storage protein gene and is expressed only in maturing seeds, it is suggested that RISBZ1 controls the expression of rice seed storage proteins. In addition, by linking the recognition sequence of the transcription factor, the GCN4 motif, in tandem and introducing it into the promoter for a gene encoding seed storage protein to facilitate its binding to the transcription factor RISBZ1, expression of a foreign gene under the control of the modified promoters is greatly enhanced.
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