A pyridoxal-phosphate protein [4]. In archaea and eukarya selenocysteine formation is achieved by a two-step process: EC?2.7.1.164?(O-phosphoseryl-tRNASec?kinase) phosphorylates the endogenous?L-seryl-tRNASec?to?O-phospho-L-seryl-tRNASec, and then this misacylated amino acid-tRNA species is converted to?L-selenocysteinyl-tRNASec?by Sep-tRNA:Sec-tRNA synthase.