Key component in the assembly and functioning of adult and embryonic striated muscles and muscle tendons. By providing connections at the level of individual microfilaments, it contributes to the fine balance of forces between the two halves of the sarcomere. The size and extensibility of the cross-links are the main determinants of sarcomere extensibility properties of muscle. In non-muscle cells, seems to play a role in chromosome condensation and chromosome segregation during mitosis. Might link the lamina network to chromatin or nuclear actin, or both during interphase. Interacts with Msp300; this interaction mediates the recruitment of Msp300 to the Z-disks. Uniformly distributed along condensed mitotic chromosomes (PubMed:9548712). Colocalizes with ball and mask in Z-lines of indirect flight muscle (PubMed:26251439). In the embryo, localizes across the muscles in a striped pattern positioned at the sites at which muscles are attached to the epidermis. In the larval body wall muscles, localizes to the Z line and is still present as a doublet at the muscle-epidermal attachment sites. During pupa development, progressively forms broad striations at the Z line which become more defined after the pupa eclosion. Expressed in the mesoderm at stage 11, several hours before myoblast fusion, and persists in most muscle cells, somatic, visceral and pharyngeal muscles and their precursors, until the third instar (PubMed:10629221, PubMed:10934048, PubMed:9548712, PubMed:10669599, PubMed:8335002, PubMed:11062264). Isoform A: Expressed in the indirect flight muscle (at protein level) (PubMed:8335002, PubMed:22467859, PubMed:26251439). Expressed both maternally and zygotically (PubMed:11062264). Expressed throughout larval, pupal and adult stages (PubMed:22467859). Flies exhibit chromosome undercondensation, chromosome breakage, loss of diploidy, and premature sister chromatid separation. They also exhibit defects in myoblast fusion, muscle organization and gut morphogenesis. Belongs to the protein kinase superfamily. CAMK Ser/Thr protein kinase family. Truncated N-terminus.