The many levels of control on bacterial selenoprotein synthesis.

Selenium shares many chemical facets with sulphur but differs from it in the redox potential, especially of the Se(2-)/S(2-) oxidation state. The higher chemical reactivity of the deprotonated selenol has been used by Biology in the synthesis of the amino acid selenocysteine and its DNA-encoded incorporation into specific positions of proteins to enhance their structural role or their activity. Since selenocysteine is a steric isomer of cysteine, numerous control mechanisms have been developed which prevent cross-intrusion of the elements during biosynthesis and insertion. As described in this review, these fidelity steps occur at the genetic, biochemical and physiological level.