Selenocysteine-specific elongation factor (EEFSEC)

Selenocysteine-specific elongation factor (EEFSEC) is a dedicated translation elongation factor that mediates the incorporation of selenocysteine—a rare amino acid—at UGA codons in eukaryotic selenoprotein mRNAs[1][2][4]. It binds selenocysteinyl-tRNA^Sec^ with high specificity and delivers it to the ribosome, enabling the co-translational insertion of selenocysteine via a unique recoding mechanism involving the SECIS (Selenocysteine Insertion Sequence) mRNA element[1][2][4]. EEFSEC differs from canonical elongation factors by its distinct domain architecture and specialized nucleotide binding properties[1]. Its action is essential for synthesizing at least 25 human selenoproteins critical for redox homeostasis, antioxidant defense, and cellular protection against oxidative stress[2]. In eukaryotes, EEFSEC works in concert with auxiliary factors such as SECIS Binding Protein 2 (SBP2), which is necessary for SECIS recognition and correct recruitment of EEFSEC to the ribosome[4][1]. The factor is found both in the cytoplasm (where it functions in translation) and the nucleus (possible additional roles not fully resolved)[2]. Dysfunction or deficiency in EEFSEC impairs selenoprotein expression, with pathological consequences in human disease contexts such as selenium deficiency syndromes and congenital defects in selenoprotein biosynthesis[2][4][1]. There are currently no known drugs that directly target EEFSEC, nor is it used as a clinical biomarker, although selenoprotein levels may indirectly reflect its cellular activity[2][4]. Safety concerns relate to its essentiality and the implications of impaired function for redox homeostasis.

Other names

Selenocysteine-specific elongation factorEEFSECSELBEFSECElongation factor secElongation factor for selenoprotein translationEukaryotic elongation factor, selenocysteine-tRNA-specificNEDPSB