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. Author manuscript; available in PMC: 2015 Feb 3.
Published in final edited form as: Angew Chem Int Ed Engl. 2014 Dec 12;54(6):1859–1863. doi: 10.1002/anie.201408817

Figure 3.

Figure 3

Triptolide binds covalently to C342 of XPB. A) MS/MS spectrum of a peptide from human XPB (TFIIH) treated with triptolide. Insets: MS/MS spectrum of m/z 730.8895, which led to the identification of a mass shift of +360.1573 Da at the Cys342 residue of 335SGVIVLPCGAGK346. The labels (b) and (y) designate N- and C-terminal fragments of the peptide, respectively. The label Δ designates (b) or (y) ions with water and/or ammonia loss. B) [3H]-triptolide does not bind covalently to recombinant C342A, C342S, or C342T XPB mutant proteins.