Serine/threonine-protein kinase which, by phosphorylating and activating mek-1, plays an important role in the activation of the JNK pathway composed of mlk-1, mek-1 and kgb-1 (PubMed:15116070, PubMed:20008556). Involved in the response to environmental stress such as heavy metals (PubMed:15116070, PubMed:18809575). By activating the JNK pathway downstream of tyrosine receptor svh-2, plays a role in axon regeneration after injury (PubMed:21670305, PubMed:23072806, PubMed:22388962). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Activated by phosphorylation at Ser-355 (PubMed:20008556). May be activated by svh-2-mediated phosphorylation (PubMed:23072806, PubMed:22388962). Interacts with max-2; the interaction is independent of max-2 and mlk-1 kinase activities (PubMed:20008556). May interact (via NPQY motif when phosphorylated on tyrosine residue) with shc-1 (via PID domain); the interaction may facilitate mek-1 phosphorylation by bringing mlk-1 and mek-1 together (PubMed:18809575). Interacts with svh-2 (via cytoplasmic domain) (PubMed:22388962). Interacts with tpa-1 (PubMed:23072806). Expressed in pharynx, intestine, hypodermis, neurons and body muscles. May be phosphorylated on tyrosine residues by svh-2. May be ubiquitinated and targeted for proteosomal degradation by E3 ubiquitin ligase rpm-1. Belongs to the protein kinase superfamily. STE Ser/Thr protein kinase family. MAP kinase kinase kinase subfamily.