Insights into the ubiquitin transfer cascade from the struct

J. Huibregste and C. Ross for advice and assistance; M. Becker and staff at National Synchrotron Light Source Beamline X25， T. Izard and L. Hendershot for comments on the manuscript. This work was supported by ALSAC， We thank P. Jeffrey， D. Minor， and T. Earnest， G. McDermott and staff at Advanced Light Source Beamline 5.0.2 for help with data collection; and P. Murray， and a Pew Scholar in Biomedical Sciences Award to B.A.S. ，。

J. Berger， the NCI Cancer Center (CORE)。