L-seryl-tRNA(Sec) kinase (PSTK) phosphorylates the serylated transfer RNA (tRNA) for Sec (Ser-tRNASec) to form Sep-tRNASec in the presence of ATP and Mg2+. PSTK exhibits a strict selectivity for Ser-tRNASec. It does not phosphorylate free Ser or Ser attached to its cognate tRNASer. This reaction involving PSTK is inferred from the equivalent reaction in mouse.
seryl-selenocysteinyl-tRNA kinase activity of PSTK:Mg2+ [cytosol]