FIG. 4.

Structural features of the substrate interaction domains of yeast and human Ubc9 proteins. (A) Ribbon diagram of yUbc9, resolved to 1.75 Å, with the active-site C₉₃ in yellow and P₁₂₃ in red. (B) Overlay of ribbon diagrams of yUbc9 (green) and hUbc9 (magenta) (PDB file 1A3S [41]). Two orientations of the active-site cysteine (yellow) were resolved in the yeast structures. (C) Close-up overlay of solid bond representations of the substrate interaction domain, residues 123 to 143 (boxed in panel B), with side chains shown for select residues and with transparent surface representation of human residues 131, 135, and 139.