Rare codon priority and its position specificity at the 5' of the gene modulates heterologous protein expression in Escherichia coli.

Rare codons and their effects in heterologous protein expression in Escherichia coli were addressed by many investigators. Here, we propose that not all rare codons of a foreign gene have negative effect but selective codon among them and its specific position in the downstream of the start codon modulates the expression. In our study, streptokinase (47 kDa), encoded by skc gene of Streptococcus equisimilis was expressed in E.