Structural component of the muscle M line which is involved in assembly and organization of sarcomere myofilaments (PubMed:15313609, PubMed:16453163, PubMed:18801371, PubMed:22621901, PubMed:23283987, PubMed:27009202). The large isoform a, isoform b, isoform d and isoform f play an essential role in maintaining the organization of sarcomeres but not myofilament alignment during body wall muscle development whereas the small isoform c and isoform d appear to have a minor role (PubMed:15313609, PubMed:16453163, PubMed:22768340). Isoform b and isoform f are required for the organization of unc-15/paramyosin into sarcomere thick filaments in body wall muscles (PubMed:27009202). By binding mel-26, a substrate adapter of the cul-3 E3 ubiquitin-protein ligase complex, regulates the organization of myosin thick filaments, likely by preventing the degradation of microtubule severing protein mei-1 (PubMed:22621901). Acts as guanine nucleotide exchange factor (GEF) for Rho GTPase rho-1 but not ced-10, mig-2 and cdc-42 (PubMed:18801371). The large isoforms regulate Ca(2+) signaling during muscle contraction by ensuring the correct localization of sarco-endoplamic reticulum Ca(2+) ATPase sca-1 and ryanodine receptor unc-68 (PubMed:22768340). By controlling the contraction and/or organization of pharyngeal muscles, plays a role in the formation of pharyngeal gland cell extension (PubMed:21868609). May interact (via fibronectin type-III domain 1, Ig-like C2-type domain 48/49 and protein kinase domain 1 or C-terminus of the interkinase region) with lim-9 (via LIM zinc-binding domain) (PubMed:19244614). May interact (via fibronectin type-III domain 1, Ig-like C2-type domain 48/49 and kinase protein domain 1 or Ig-like C2-type domain 50, fibronectin type-III domain 2 and kinase protein domain 2) with scpl-1 isoforms a and b (via FCP1 homology domain); the interaction may act as a molecular bridge to bring two unc-89 molecules together or to stabilize a loop between the 2 kinase domains (PubMed:18337465, PubMed:19244614). May interact (via SH3 domain) with unc-15 (PubMed:27009202). May interact (via Ig-like C2-type domain 1-3) with cpna-1 (via VWFA domain) (PubMed:23283987). May interact (via Ig-like C2-type domain 2/3 and, Ig-like C2-type domain 50 and fibronectin type-III domain 2) with mel-26 (via MATH domain) (PubMed:22621901). May interact (via DH and PH domains) with rho-1, ced-10, mig-2 and cdc-42 (PubMed:18801371). Colocalizes with scpl-1 (isoform b) to the M line (PubMed:19244614). Colocalizes with cpna-1 to the M line (PubMed:23283987). Colocalizes with mel-26 to the M line (PubMed:22621901). Accumulates at the center of thick myofilaments in M line-like structures in myoepithelial sheath cells (PubMed:17326220). Expressed in body-wall, pharyngeal muscles and a few muscle cells of the tail (at protein level) (PubMed:8603916, PubMed:18337465, PubMed:19244614, PubMed:22621901, PubMed:22768340, PubMed:23283987, PubMed:27009202). Expressed in gonadal myoepithelial sheath cells (at protein level) (PubMed:17326220). Isoform c: Expressed in body wall and vulval muscles but not in pharyngeal muscles (PubMed:15313609). Isoform d: Specifically expressed in vulval, intestinal, anal depressor and anal sphincter muscles (PubMed:15313609). Expressed in embryos (PubMed:23283987). Isoform a: Expressed in embryo, throughout larval development and in adults (PubMed:15313609). Isoform b: Expressed in embryo, throughout larval development and in adults and is one of the most abundant (PubMed:15313609). Isoform c: Expressed in embryo, throughout larval development and in adults and is one of the most abundant (PubMed:15313609). Isoform d: Expressed in embryo, throughout larval development and in adults (PubMed:15313609). Protein kinase domains 1 and 2 are predicted to be catalytically inactive (PubMed:16453163). The two kinase domains are required for the organization of thick filament component myosin heavy chain myo-3 but not of myosin heavy chain unc-54 and unc-15/paramyosin (PubMed:27009202). The SH3 domain is required for the organization of thick filament components myosin heavy chain unc-54 and myo-3 and unc-15/paramyosin. The PH domain does not bind inositol 1,4,5-trisphosphate. The PH domain has an unusual closed conformation of the lipid binding site which is lined by negative charged amino acids which probably prevents binding to membrane lipids. Mutants lacking isoform a, isoform b, isoform e and isoform f have an abnormal organization of the myofilament lattice of body wall and pharyngeal muscles (PubMed:16453163, PubMed:18801371, PubMed:22621901, PubMed:27009202). In body wall muscles, unc-15/paramyosin accumulates in large foci outside thick filaments and myosin heavy chains unc-54 and myo-3 fail to assemble into parallel myofibrils (PubMed:27009202). In addition, myosin thick filaments are disorganized with the formation of abnormal myosin heavy chain myo-3 aggregates and V-shaped crossing of A bands (PubMed:18801371, PubMed:22621901). In mutants lacking isoform b, isoform c, isoform d and isoform f, myo-3 fails to assemble into parallel myofibrils whereas unc-54 and unc-15 localization is normal (PubMed:27009202). Mutants lacking isoform b, isoform c, isoform d and isoform f have defects only in body wall muscle structure (PubMed:16453163). RNAi-mediated knockdown of isoform a or isoform b, isoform c and isoform d causes similar defects in the organization although RNAi-mediated knockdown of isoform c causes a less severe defect in myofilament organization (PubMed:15313609). In mutants lacking isoform a, isoform b, isoform e and isoform f, mei-1 protein levels are decreased by 20 percent (PubMed:22621901). RNAi-mediated knockdown of isoform a, isoform b, isoform e and isoform f but not of isoforms c and d disrupts sca-1 localization to linear punctate structures along in the M line in body wall muscles (PubMed:22768340). RNAi-mediated knockdown has no effect on ovulation (PubMed:17326220). Belongs to the protein kinase superfamily. CAMK Ser/Thr protein kinase family. In contrast to obscurins in other species, unlikely to have serine/threonine kinase activity as both protein kinase domains are predicted to be catalytically inactive. The Lys residue involved in ATP binding is not conserved in both kinase domains.