ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Binding of GTP stimulates kinase activity. Homodimer. Belongs to the protein kinase superfamily. TKL Ser/Thr protein kinase family. ROCO subfamily. The cDNA contains a duplication of exon 3. Truncated N-terminus. Truncated N-terminus.