Required for hypodermal cell fusion, together with cdc-42 and ced-10, leading to embryonic body elongation, which involves dramatic cytoskeletal reorganization (PubMed:8824291). Plays a redundant role with max-2 in dorsal axonal guidance in ventral cord commissural motoneurons and in P neuroblast migration. Acts probably downstream of Rho GTPases mig-2 and ced-10 to regulate these 2 processes (PubMed:17050621). Involved in orientating axonal growth of HSN neurons (PubMed:18499456). During gonad morphogenesis and probably in association with pix-1 and git-1, involved in the migration of distal tip cell (DTC) and in maintaining their sharp tapering morphology. In addition, plays a redundant role with max-2 in DTC-mediated guidance of gonad elongation (PubMed:19023419, PubMed:19797046). May phosphorylate mlc-4 (PubMed:19675126). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Divalent cations such as magnesium or manganese. Interacts with cdc-42 (GTP-bound form) and cedd-10 (GTP-bound form). Co-localizes with ced-10/rac-1 and cdc-42 at hypodermal cell boundaries during embryo elongation (PubMed:8824291). Preferentially enriched at pharyngeal muscle cells boundaries (PubMed:9535804). In CAN neurons, detected in the cell bodies and along the axons (PubMed:9535804). Remains diffused in the cytoplasm during distal tip cell (DTC) migration (PubMed:19023419). Specifically colocalized with cdc-42 and ced-10 at all hypodermal cell boundaries during embryo elongation throughout the second phase of embryogenesis. Expressed mainly in pharyngeal muscles, the CAN neurons, motor neurons in the ventral nerve cord, several cells in the tail region (including the B and Y cells from L1 to adult, the hypodermal blast cell T in the L1 and some of its progeny in later stages), and the distal tip cells. Highly expressed at the embryonic stage, with decreasing expression from L1 onwards. In pak-1 and pak-2 double mutants, defects in embryogenesis and L1 stage lethality. The few animals reaching adulthood have normal ventral cord commissural motoneuron axonal guidance and are relatively coordinated. In max-2 and pak-1 double mutants, DD and DC motoneuron axons fail to reach the dorsal cord (PubMed:17050621). Animals are also uncoordinated, defective in egg laying and in distal tip cell (DTC) migration, guidance and morphology, and exhibit ventral enclosure defects (PubMed:17050621, PubMed:19023419). Belongs to the protein kinase superfamily. STE Ser/Thr protein kinase family. STE20 subfamily.