Supplementary Figure 1: Schemes show two major hurdles in the ubiquitin field.
From: A bacterial genetic selection system for ubiquitylation cascade discovery
The two pose challenges in assigning specific associations of components along ubiquitin cascades. (a) Ubiquitylation is rapidly reversed by deubiquitylases. In human there are about hundred deubiquitylating enzymes (DUBs) which efficiently and rapidly remove the ubiquitin moiety from targeted proteins. (b) Ubiquitylation cascades are multiplex. For example eight different substrates were found for the BRCA1 E3-ligase. Similarly, 7 different E3-ligases were demonstrated to ubiquitylate p53.
