Phosphoseryl tRNA Kinase (PSTK)

In eukaryotes, decoding of the UGA codon as selenocysteine (Sec) requires a Sec insertion sequence (SECIS) in the 3-prime untranslated region of the mRNA. A specific elongation factor, EFSEC, specifically recognizes selenocysteyl-tRNA(Ser)Sec and the SECIS and directs insertion of Sec into protein.The PSTK cDNA was isolated and cloned into a His-tag expression vector. The deduced human PSTK protein contains 359 amino acids with a predicted ATP-binding domain.PSTK specifically catalyzed the formation of phosphoseryl-tRNA(Ser)Sec from seryl-tRNA(Ser)Sec and ATP in the presence of Mg2+. In binding assays, both tRNA(Ser)Sec and seryl-tRNA(Ser)Sec bound to PSTK, but ATP enhanced the binding of tRNA(Ser)Sec and decreased the binding of seryl-tRNA(Ser)Sec.