Possible non-essential role in spermiogenesis. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] ATP + L-tyrosyl-[protein] = ADP + H(+) + O-phospho-L-tyrosyl-[protein] Autophosphorylation on Tyr-264 in the activation loop is required for kinase activity. May be due to a competing acceptor splice site. Due to an alternative splicing donor site in exon 19. Markedly reduced enzymatic activity. Belongs to the protein kinase superfamily. CMGC Ser/Thr protein kinase family. MNB/DYRK subfamily.