Switches, excitable responses and oscillations in the Ring1B/Bmi1 ubiquitination system

PLoS Comput Biol. 2011 Dec;7(12):e1002317. doi: 10.1371/journal.pcbi.1002317. Epub 2011 Dec 15.

Abstract

In an active, self-ubiquitinated state, the Ring1B ligase monoubiquitinates histone H2A playing a critical role in Polycomb-mediated gene silencing. Following ubiquitination by external ligases, Ring1B is targeted for proteosomal degradation. Using biochemical data and computational modeling, we show that the Ring1B ligase can exhibit abrupt switches, overshoot transitions and self-perpetuating oscillations between its distinct ubiquitination and activity states. These different Ring1B states display canonical or multiply branched, atypical polyubiquitin chains and involve association with the Polycomb-group protein Bmi1. Bistable switches and oscillations may lead to all-or-none histone H2A monoubiquitination rates and result in discrete periods of gene (in)activity. Switches, overshoots and oscillations in Ring1B catalytic activity and proteosomal degradation are controlled by the abundances of Bmi1 and Ring1B, and the activities and abundances of external ligases and deubiquitinases, such as E6-AP and USP7.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Computer Simulation
  • Gene Silencing
  • Nuclear Proteins / genetics
  • Nuclear Proteins / metabolism*
  • Polycomb-Group Proteins
  • Proteasome Endopeptidase Complex / genetics
  • Proteasome Endopeptidase Complex / metabolism
  • Repressor Proteins / genetics
  • Repressor Proteins / metabolism
  • Ubiquitin / metabolism*
  • Ubiquitin-Protein Ligases / genetics
  • Ubiquitin-Protein Ligases / metabolism*
  • Ubiquitination

Substances

  • Nuclear Proteins
  • Polycomb-Group Proteins
  • Repressor Proteins
  • Ubiquitin
  • Ubiquitin-Protein Ligases
  • Proteasome Endopeptidase Complex