A synergistic effect of suppressive CGG codon in +2 position and downstream CAT repeats for efficient heterologous protein expression in Escherichia coli

The negative effect of NGG codons at +2 position has been well documented for the down regulation of recombinant protein expression in Escherichia coli. But this is not true when certain specific sequences are present in the downstream of NGG codons. This has been proved in our study while expressing human Erythropoietin (EPO) in E. coli GJ1158. Towards this, nine recombinant constructs were made and their expression profile was compared. In our results, we found that the suppressive nature of NGG codon (GGG, CGG) in the +2 position was overcome by imposing a downstream CAT repeat motif. The expression of EPO levels is higher in the constructs having the combination of both CGG codon at 2nd position and CAT repeats than the other constructs having either CGG or CAT repeat alone. In addition, it is also interesting to note that increasing number of CAT repeats shows increased expression levels.