Regulation of Signaling by Non-degradative Ubiquitination

A central unifying principle in the field of signal transduction has been the covalent modification of proteins by phosphorylation. A wide range of protein kinases are known, and the process is regulated by a more limited although important number of protein phosphatases. Recently, there has been a remarkable increase in the numbers of examples of another reversible covalent modification in proteins during signaling, ubiquitination. Historically, the function of ubiquitination was to cause protein degradation in the 26 S proteasome.