SecISbinding

SECIS-binding refers to the interaction between SECIS elements in selenoprotein mRNAs and specialized proteins that recognize and bind these RNA elements to facilitate the incorporation of selenocysteine at UGA codons during translation. This binding is a key step in allowing the ribosome to reinterpret a stop signal as an amino acid, enabling the production of selenoproteins that often contribute to redox biology and antioxidant defense.

In bacteria, the main factor is SelB, a GTPase that binds both Sec-tRNA and the bacterial SECIS element, coordinating the delivery of selenocysteine to the ribosome at the UGA codon. In archaea and eukaryotes, the SECIS element is typically located in the 3' untranslated region of the mRNA, and SECIS-binding protein 2 (SBP2) binds to this element. SBP2 then interfaces with the Sec-specific elongation factor eEFSec and Sec-tRNA^[Sec] to recruit the selenocysteine insertion machinery to the ribosome.

The SECIS elements themselves are conserved RNA structures, but their sequence and structural details differ among bacteria, archaea, and eukaryotes. The binding interactions are context-dependent and can be influenced by additional proteins and RNA features that modulate efficiency and fidelity of selenocysteine incorporation.

Disruptions in SECIS-binding, such as mutations in SBP2, can impair selenoprotein synthesis and have physiological consequences in humans. Understanding SECIS-binding sheds light on the unique decoding of UGA codons and the regulation of selenoprotein expression across different life forms. See also selenocysteine, SECIS element, SBP2, SelB, and eEFSec.