ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] [DNA-directed RNA polymerase] + ATP = ADP + H(+) + phospho-[DNA-directed RNA polymerase] Expressed in the dividing region of the root apex and in differentiated cells such as those in the sclerenchyma, pericycle and parenchyma of the central cylinder. Expressed in the intercalary meristem and the elongation zone of internodes. Expression reaches a peak in the G1/S phases and then decreases in the G2/M phases. By gibberellic acid (GA3) and submergence. Down-regulated by auxin. Belongs to the protein kinase superfamily. CMGC Ser/Thr protein kinase family. CDC2/CDKX subfamily.