Defining serine tRNA knockout as a strategy for effective repression of gene expression in organisms with a recoded genome.

Whole genome codon compression-the reassignment of all instances of a specific codon to synonymous codons-can generate organisms capable of tolerating knockout of otherwise essential transfer RNAs (tRNAs). As a result, such knockout strains enable numerous unique applications, such as high-efficiency production of DNA encoding extremely toxic genes or non-canonical proteins. However, achieving stringent control over protein expression in these organisms remains challenging, particularly with proteins where incomplete repression results in deleterious phenotypes.