Central component of the condensin complex, a complex required for conversion of interphase chromatin into mitotic-like condense chromosomes. The condensin complex probably introduces positive supercoils into relaxed DNA in the presence of type I topoisomerases and converts nicked DNA into positive knotted forms in the presence of type II topoisomerases (By similarity). Forms a heterodimer with smc2. Component of the condensin complex, which contains the smc2-smc4 heterodimer (By similarity). The SMC hinge domain, which separates the large intramolecular coiled coil regions, allows the heterodimerization with smc2 forming a V-shaped heterodimer. Belongs to the SMC family. SMC4 subfamily.