SecISbindenden

SecISbindenden refers to the class of factors that recognize and bind the SecIS element, a characteristic RNA structure found in the 3' untranslated region of selenoprotein mRNAs. The SecIS element serves as a cis-acting signal that enables the recoding of the UGA stop codon as selenocysteine during translation. SecISbinding factors are essential for coordinating the incorporation of selenium into selenocysteine and for recruiting the specialized machinery that supports this process.

In bacteria, the primary SecISbinding factor is SelB, a ribosome-associated, GTP-binding protein. SelB binds both the Sec-tRNA[supSec] and the SecIS element, delivering selenocysteyl-tRNA to the ribosome when a UGA codon is encountered. The interaction between SelB, the SecIS element, and the ribosome coordinates translation elongation with selenocysteine incorporation, ensuring accurate expression of bacterial selenoproteins.

In archaea and eukaryotes, SecISbinding involves different but related components. Eukaryotes utilize SBP2 (SECIS-binding protein 2), which binds the SECIS element in the 3'UTR and interfaces with the rest of the selenocysteine incorporation machinery, including specialized elongation factors and the Sec-tRNA. Archaea employ homologous factors, often with variations that reflect domain-specific adaptations, to achieve a similar outcome.

SecISbinding factors are conserved across organisms that encode selenoproteins, and mutations or regulatory changes affecting these factors can influence the expression and activity of the entire selenoproteome. The concept underscores a key step in the specialized translation pathway that expands the genetic code to include selenocysteine.