“…Additionally, a recent ABPP-based covalent screen against purified RNF4, a RING-domain E3 ligase identified new covalent fragments that target this protein. 114,115 The most promising hit TRH 1-23 was shown to label either Cys132 or Cys135, two cysteine residues that form one of zinc-coordinating sites within the RING domain. Although disrupting either one of these sites through mutagenesis was previously shown to inhibit RNF4 function, Ward et al included evidence to suggest that RNF4 retains in vitro self-ubiquitination activity, suggesting that TRH 1-23 did not disrupt RNF4 E3 ligase function.…”