Unusual effect of clusters of rare arginine (AGG) codons on the expression of human interferon α1 gene in Escherichia Coli

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The human interferon (hIFNα 1) gene contains 11 arginine (Arg) codons AGG or AGA, which are extremely rare for bacteria, four of which are organized in tandems. The two AGG tandems (corresponding to Arg 12 Arg 13 and Arg 163 Arg 164) are known to inhibit the translation of hIFNα 1 mRNA and therefore they are considered to be responsible for the poor expression of hIFNα 1 gene in bacterial cells. To study the effect of these two tandems on the expression of hIFNα 1 in E. coli, four new gene variants were designed to contain preferential Arg codons (CGT) substituted for the rare AGG codons in either the first, the second or both AGG tandems. We found that, whereas the yield of hIFNα 1 protein per cell remained unchanged, the level of hIFNα 1 mRNA decreased gradually (by a factor of two) with the consecutive substitution of the first, second and both AGG tandems. These results indicated, first, that the AGG clusters might have a stabilizing effect on the mRNA, and second, that mRNAs devoid of such clusters were translated at a higher rate in vivo. The protein products of the four genes (having the same amino acid sequence) showed different specific antiviral activity. The most active was the product of gene hIFNα 1(c) in which the second AGG tandem (corresponding to Arg 163, Arg 164) was preserved while the least active was the protein of gene hIFNα 1(d) (devoid of both AGG clusters). The role of the AGG tandems in folding of the gene product is discussed.