Abstract
Rice OsMac1 gene contained a 5'untranslational region (5'UTR) consisting of an approximately 500 bases upstream of the major ORF. This region contained three upstream ORFs (uORFs), and CU rich region. We found three forms of 5'UTR, named as UTRa, UTRb, and UTRc, which were derived from alternative splicing on the junction between Exon1 and Exon2. UTRa and UTRb was 54 and 38 base shorter than UTRc, respectively. These sequences were expected to be involved in control of translation of the major ORF. A reporter gene, in which the GUS gene was connected downstream the UTRc, was expressed with a high translational efficiency, but GUS genes connected with UTRa and UTRb resulted in a low translational efficiency as shown in those without 5'UTR. Deletion of the CU rich region resulted in decrease of the translation of the major ORF. In contrast, the GUS gene attached with modified 5'UTRs, in which the initiation codons of uORFs were defected, showed no significant changes on the GUS activities. These results suggest that the 5'UTR possesses two kinds of the enhance sequences, the CU rich region and the 38 bp region, affecting the efficiency of the translation of the major ORF.
