Cell adhesion and signal transduction are coordinated processes that may be linked through regulatory elements such as actin-binding proteins. One such protein that may fulfill this role is coronin. In Dictyostelium discoideum, coronin is involved in cellular processes such as mitosis, cell motility, and phagocytosis. In addition, a human coronin, p57, has been described which interacts with the p47 component of phox proteins and may be involved in the formation of phagocytic vacuoles. Here, we describe a family of four mouse proteins which share 38% identity with Dictyostelium coronin and thus are designated coronin-1, -2, -3, and -4. The gene for coronin-2 is localized to mouse chromosome 19, 5' of the gene for CD45-associated protein. All the coronin proteins contain five highly conserved WD domains. However, their carboxyl regions are quite distinct. Three of the four proteins are ubiquitously expressed, whereas coronin-1, the mouse ortholog of p57, demonstrates expression restricted to hematopoietic cells. Comparison of expressed sequence tag cDNAs indicates that coronin-1, -2, -3, and -4 are highly conserved between mice and humans.