Part of the Wnt signaling pathway essential for the specification of the mesodermal cell fate in early embryos. Stimulates the wrm-1/lit-1-dependent phosphorylation of pop-1 and plays a role in the initial nuclear accumulation of wrm-1 (By similarity). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Interacts with, and is activated by, tap-1. Belongs to the protein kinase superfamily. STE Ser/Thr protein kinase family. MAP kinase kinase kinase subfamily.