Central component of the condensin I complex, a complex required for conversion of interphase chromatin into mitotic-like condense chromosomes (PubMed:11914278, PubMed:19781752). The condensin I complex introduces positive supercoils into relaxed DNA in the presence of type I topoisomerases (PubMed:11914278). Converts nicked DNA into positive knotted forms in the presence of type II topoisomerases (By similarity). Also a central component of the condensin II complex, a complex that seems to play a role in prophase chromosome condensation (PubMed:19119011, PubMed:19781752). Both the condensin complex I and II play a role in meiotic and mitotic chromosome segregation (PubMed:11914278, PubMed:19119011, PubMed:23684975). Plays a role in robust cytokinesis upon the presence of chromatin obstructions (PubMed:23684975). Component of the condensin I complex, which contains the mix-1/SMC2 and smc-4/SMC4 heterodimer, and three non SMC subunits that probably regulate the complex: dpy-26, capg-1 and dpy-28 (PubMed:19119011, PubMed:11914278, PubMed:19781752). Within the complex, interacts with mix-1, dpy-26, capg-1 and dpy-28 (PubMed:11914278, PubMed:19781752, PubMed:19119011, PubMed:28301465). Component of the condensin II complex, which contains the mix-1/SMC2 and smc-4/SMC4 heterodimer, and three non SMC subunits, kle-2, capg-2 and hcp-6 that probably regulate the complex (PubMed:19781752, PubMed:19119011). Within the complex, interacts with mix-1, kle-2, capg-2 and hcp-6 (PubMed:19781752, PubMed:19119011, PubMed:28301465). Interacts with smcl-1 (PubMed:28301465). Localizes to condensed chromosomes during mitosis and meiosis. Localizes to chromosomes in a faint speckled pattern during prophase, then appears in two stripes outlining each chromosome during prometaphase. During metaphase, localizes at the poleward face of the condensed chromosomes. Dissociation from chromosomes is observed in late telophase. The flexible SMC hinge domain, which separates the large intramolecular coiled coil regions, allows the heterodimerization with mix-1, forming a V-shaped heterodimer. RNAi-mediated knockdown disrupts prometaphase chromosome organization and chromosome segregation in mitosis and meiosis II and leads to aneuploidy throughout development (PubMed:11914278, PubMed:23684975). Disrupts mix-1 localization to mitotic chromosomes (PubMed:11914278). Increased levels of phosphorylated air-2 at the spindle midzone, indicating activation of the abscission checkpoint (PubMed:23684975). Results in cleavage furrow regression and failed cytokinesis during the first and second embryonic divisions (PubMed:23684975). Belongs to the SMC family. SMC4 subfamily.