THE 3'-UNTRANSLATED REGION OF A RICE ALPHA-AMYLASE GENE MEDIATES SUGAR-DEPENDENT ABUNDANCE OF MESSENGER-RNA

A decrease in transcript stability is one of the important mechanisms that control the sugar repression of alpha-amylase gene expression in rice suspension cells. In this study, we investigated the function of the 3' untranslated region (3'UTR) of a rice alpha-amylase gene, alpha Amy3, in relation to sugar-dependent accumulation of mRNA. By examini ng the transient expression of chimeric genes in rice protoplasts, we were able to demonstrate that the aAmy3 3'UTR mediated the sugar-depen dent repression of fused heterologous gene expression. The same kineti cs of accumulation of aAmy3 mRNA and reporter mRMA carrying the aAmy3 3'UTR in response to glucose deprivation were observed, suggesting tha t the alpha Amy3 3'UTR is sufficient, and probably the major determina nt for controlling the abundance of these transcripts. Functional anal ysis of two subdomains of alpha Amy3 3'UTR by insertion into a sugar-i nducible chimeric gene confirmed their roles in sugar repressibility. The regulatory sequences in the alpha Amy3 3'UTR may act as potent det erminants of mRNA stability in response to sugar availability. This fi nding has important implications for studying the regulatory mechanism of sugar repression in eukaryotes.