Abstract
It is shown that in immunological, structural and functional terms the uncoating protein, which catalyses ATP‐dependent dissociation of clathrin triskelia from clathrin‐coated vesicles is intimately related to two major stress proteins of mammalian cells. These proteins of hitherto unknown functions have polypeptide mol. wts. of 73 kd and 72 kd, respectively. They are normal cell constituents which are synthesized in increased abundance under adverse environmental circumstances, such as non‐physiological temperatures or treatment with amino acid analogues.