Coat formation in coated vesicles.

The proteins of Mr 100 000-110 000 present in the protein coat of coated vesicles have been shown to facilitate formation of a homogeneous small-size basket (coat) when added to clathrin [Zaremba, S., & Keen, J.H. (1983) J. Cell Biol. 97, 1339]. We have prepared this protein of coat proteins by two different methods and shown that they are very important for the binding of clathrin to uncoated vesicles to form coated vesicles. By labeling the three components (clathrin, 100 000-110 000 proteins, and uncoated vesicles) with different fluorescent markers and analyzing their distribution on sucrose gradients, we have been able to determine the composition of the products formed. In the presence of the 100 000-100 000 fraction of coat proteins, not only does the size distribution of the clathrin basket become uniform but also the rate of polymerization is strongly increased.