Side effects of extra tRNA supplied in a typical bacterial protein production scenario

Recombinant protein production is at the core of biotechnology and numerous molecular tools and bacterial strains have been developed to make the process more efficient. One commonly used generic solution is to supply extra copies of low-abundance tRNAs to compensate for the presence of complementary rare codons in genes-of-interest. Here we show that such extra tRNA, supplied by the commonly used pLysSRARE2 plasmid, can cause two side effects: (1) growth and gene expression can be impaired, and (2) apparent positive effects can be caused by differential expression of the lysozyme gene encoded on the same plasmid and not the tRNAs per se. These phenomena seem to have been largely overlooked despite the huge popularity of the T7/pET-based systems for bacterial protein production.