FIG. 3.

hHR23 protects E6-ubiquitylated p53 from deubiquitylation. (A) Radiolabeled p53 was ubiquitylated by Hdm2 or by E6/E6-AP as indicated. After 1 h, the reactions were stopped by the addition of EDTA, and the deubiquitylation reaction was started by the addition of the ubiquitin-specific protease UBP1 in the absence (−) or in the presence (+) of hHR23 or its deletion mutants or the Uba domain of Chap1/hPlic-2 as indicated. Similarly, the effect of UBP1 on auto-ubiquitylated Hdm2 (B) and on E6-AP-ubiquitylated Hrs (C) was tested. Ubiquitylated forms of the respective radiolabeled proteins are indicated by a double asterisk.