AbstractThe two subunits of the het‐erodimeric protein cop32/34, an actin‐binding protein, are encoded by separate single‐copy genes. We have established the genomic structure of both genes. A sequence comparison of cap32/34 with capZ from chicken skeletal muscle and two partially known sequences fromSaccharomyces cerevisiaeandXenopus laevisshow that heterodimeric capping proteins belong to a highly conserved group of actin‐binding proteins. This conclusion is supported by the cross‐reaction of polyclonal antibodies against cap32 and cap34 with proteins from lower and higher eukaryotes. In addition, a system is presented that allows the expression of truncated cap34 polypeptides under the control of the cap34