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The relationship between the codon usage bias, gene expression level and the AUG context(from -20 to +6 positions relative to the initiator AUG codon) was examined in 541unigene sequences of rice. A significant correlation for CAI values (codon adaptationindex) was observed at five nucleotide positions (-19, -18, -9, -4, +5), eight (-19, -18,-14, -9, -6, -4, -1, +5) for CPP (codon preference parameter), and seven (-18, -16, -15,-9, -7, -1, +6) for mRNA abundance in the flanking sequence of the initiator AUG codonrespectively, but a significantly positive correlation for both CAI and CPP at twopositions (-4 and +5), indicating that both those positions are evolutionally under thenatural selection constraint at the translational level. By site-directed mutagenesis atseven specific positions (-18, -16, -15, -9, -7, -1 and +6) for allergenic protein thathad the highest mRNA abundance in this study, its expression level decreased dramatically63.3 and 72.5% respectively, indicating the importance of those 7 positions for geneexpression. A highly positive correlation (r=0.625, P<0.01) between AUGCAI and GCcontent in the flanking sequence of the initiator AUG codon showed a more effectivehigher GC content on translation initiation efficiency. The strong preference for G orC at those 8 positions (-6, -5, -3, -2, -1, +4, +5 and +6) in the AUG context suggestedthat an important factor in modulation of the translation efficiency, as well assynonymous codon usage bias, particularly in highly expressed genes.
The relationship between the codon usage bias, gene expression level and the AUG context (from -20 to +6 positions relative to the initiator AUG codon) was examined in 541unigene sequences of rice. A significant correlation for CAI values (codon adaptation index) was observed (-19, -18, -9, -4, +5), eight (-19, -18, -14, -9, -6, -4, -1, +5) for CPP ( codon preference parameter, and seven (-18, -16, -15, -9, -7, -1, +6) for mRNA abundance in the flanking sequence of the initiator AUG codonrespectively, but a significant positive correlation for both CAI and CPP at twopositions (-4 and +5), indicating that both those positions are evolutionally under thenatural selection constraint at the translational level. By site-directed mutagenesis at seven specific positions (-18, -16, -15, -9, - 7, -1 and +6) for allergenic protein that the highest mRNA abundance in this study, its expression level decreased dramatically63.3 and 72.5% respectively, indicating the impor A highly positive correlation (r = 0.625, P <0.01) between AUGCAI and GC content in the flanking sequence of the initiator AUG codon showed a more efficient glycope GC content on translation initiation efficiency. The strong preference for G orC at those 8 positions (-6, -5, -3, -2, -1, +4, +5 and +6) in the AUG context suggested that an important factor in modulation of the translation efficiency, as well assynonymous codon usage bias, particularly in highly expressed genes.