The coatomer complex is involved in intracellular protein transport and comprises an assembly of seven polypeptide subunits designated alpha, beta, beta', gamma, delta, epsilon, and zeta COP. Rooted phylogenetic trees constructed from the full-length cDNA and amino acid sequences of 49 COP entities in different eukaryotes from yeast to man generally revealed striking conservation of each subunit through evolution. Both nucleotide and protein trees displayed close relationships between alpha and beta' subunits, between beta and gamma subunits, and between delta and zeta subunits, implying evolution from common ancestors as well as functional similarity. Interestingly, although 6 out of 7 epsilon-COP genes appeared to be grouped and related to the beta-COP genes, 4 out of 7 epsilon