Figure 1. Mechanisms of ubiquitylation on chromatin.

(A) Structural changes: attachment of ubiquitin interferes with chromatin compaction. (B) Recruitment: monoubiquitin or non-degradatory polyubiquitin chains serve as a docking site for recruiting other factors to chromatin. (C) Degradation: polyubiquitin such as Lys 11 or Lys 48-linked chains serve as a recognition signal for proteasomal degradation. Note that the spectrum of ubiquitylated substrates is not restricted to histone proteins but includes also other chromatin-associated factors. K, lysine (Lys).