RARE CODONS AND GENE-EXPRESSION IN ESCHERICHIA-COLI

The effect of rare codons on gene expression in Escherichia coli was i nvestigated. A chimeric gene consisting of the CAT gene and a fragment of the gene coding for the alpha-domain of beta-galactosidase was des igned. Synthetic oligonucleotides were inserted into different sites o f the chimeric gene. These oligonucleotides were constructed so that w hile coding for identical amino acid sequences, they contained various combinations of arginine codons AGG, AGA, and CGT. It was shown that both the presence of rare arginine codons (AGG and AGA) in the templat e and their relative position have a significant effect on the level o f gene expression. The presence of rare leucine, isoleucine, glycine, and proline codons does not produce such an effect. The translation of AGGAGG and AGAAGA sequences was shown to produce a significant amount of polypeptides of incomplete length. The existence of such clusters of identical rare codons affects the length of the specific template R NA. The given system of chimeric genes is a sensitive and easily detec ted reporter system for studying the translation of rare codon cluster s.