TRNAU1AP (tRNA selenocysteine 1 associated protein 1), also known as SECp43, is a pivotal regulator of selenocysteine biosynthesis and incorporation into selenoproteins. Mechanistically, TRNAU1AP stabilizes the complex of SECISBP2, EEFSEC, and tRNA(Sec), facilitating cotranslational selenocysteine incorporation at UGA codons 1. The protein interacts with selenocysteyl-tRNA(Ser)Sec-EFsec complexes and promotes interactions between EFsec and SBP2, enhancing selenoprotein synthesis efficiency 1. Beyond its canonical selenoprotein function, TRNAU1AP exhibits broader cellular roles: it modulates alternative splicing of hundreds of endogenous genes 2 and participates in cell proliferation and migration through the PI3K/Akt signaling pathway 3. Functionally, TRNAU1AP knockdown reduces selenoprotein expression levels, impairing cell proliferation and migration in embryonic and trophoblast cells 3. Clinically, TRNAU1AP deficiency models demonstrate relevance to renal fibrosis pathogenesis, where selenium deficiency-induced reductions in TRNAU1AP expression correlate with elevated oxidative stress, mitochondrial dysfunction, and activation of the Wnt/β-catenin pathway 45. Additionally, TRNAU1AP fusion proteins have been identified in papillary thyroid carcinomas 6, suggesting potential oncogenic relevance.