The phosphorylation and dephosphorylation of proteins on serine and threonine residues is an essential means of regulating a broad range of cellular functions in eukaryotes, including cell division, homeostasis and apoptosis. A group of proteins that are intimately involved in this process are the serine/threonine (Ser/Thr) protein kinases. PRKY (protein kinase, Y-linked) and PRKX (protein kinase, X-linked) are members of the Ser/Thr protein kinase family, both of which belong to the subfamily of cAMP-dependent kinases. Encoded by a gene that is located near the pseudoautosomal region on chromosome Y, PRKY contains one protein kinase domain through which it catalyzes the ATP-dependent phosphorylation of target proteins. Functioning in a similar manner to PRXY, PRKX contains one protein kinase domain and is essential for macrophage differentiation and renal epithelial cell migration. Defects in the genes encoding PRKY and PRXX are associated with sex reversal disorder, namely XX in males and XY in females.