FIG. 4.

Three-dimensional molecular models of CROC-1 (middle) and TSG101 (right), built on the basis of the experimental three-dimensional structure of S. cerevisiae UBC4 (12) (left). The critical Cys, essential for the catalytic activity of ubiquitin-conjugating enzymes, is highlighted in the latter. Beta pleated sheets are represented as flat arrows, and alpha helices are represented as barrels. The models were built on sequences that could be aligned with UBC4, and thus the amino terminus (N-term) of CROC-1 and the carboxy terminus (C-term) of TSG101 are not represented.