Fig. 1. Structural comparison of Nedd4/Rsp5 family proteins. (A) Schematic representation of the domain structures. The C2, WW and HECT domains are indicated by shaded, hatched and black boxes, respectively. A.A., amino acids. (B) Amino-acid sequence alignment of the HECT domains. Amino acids that are identical in Pub2p are indicated by dark shading. The asterisk indicates the conserved cysteine residue (Cys639 for Pub2p), which is required for the thioester bond formation with the C-terminal glycine residue of ubiquitin. hNedd4 and mNedd4 indicate human and mouse Nedd4p, respectively. E6-AP is a prototype HECT-type ubiquitin-protein ligase from human. (C) A phylogenetic tree of HECT domains, constructed by the UPGMA method, of seven HECT-type ubiquitin ligases of S. pombe and Rsp5p of S. cerevisiae.