Figure 1. Shown is the equilibrium between ubiquitinated states of the RNA polymerase I complex, and the consequences of these differences in ubiquitination on the stability of the Polymerase I complex. The identity of the ubiquitin proteases that promote the deubiquitination reactions is indicated. Ubi1 and Ubi2 would correspond to the different ubiquitinated states, which would result in RNAP I degradation and nuclear retention, respectively.