ABSTRACT
Selenoproteins are found in all kingdoms of life, albeit not all organisms, and confer unique features to such proteins due to the chemical nature of selenocysteine (Sec), and the defining entity of selenoproteins. Because Sec is cotranslationally inserted at an inframe UGA stop codon by dedicated selenoprotein translation machinery interacting with a secondary structure of the mRNA (called a Sec Insertion Sequence (SECIS) element), heterologous selenoproteins cannot be expressed in recombinant form in E. coli using traditional methods typically compatible with non-selenoproteins. The authors used a new strain of E. coli that has its 321 chromosomal TGA codons exchanged for TAG and its release factor RF1 genetically deleted. Together with the redefinition of the tRNA for Sec with the corresponding anticodon, they produced recombinant TrxR1 with nearly full Sec content when combined with a variant of the previously designed and tailored SECIS element.
