E3 ligase activity of RING finger proteins that interact with Hip‐2, a human ubiquitin‐conjugating enzyme

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Abstract
To identify proteins that interact with Huntingtin‐interacting protein‐2 (Hip‐2), a ubiquitin‐conjugating enzyme, a yeast two‐hybrid screen system was used to isolate five positive clones. Sequence analyses showed that, with one exception, all Hip‐2‐interacting proteins contained the RING finger motifs. The interaction of Hip‐2 with RNF2, one of the clones, was further confirmed through in vitro and in vivo experiments. Mutations in the RING domain of RNF2 prevented the clone from binding to Hip‐2, an indication that the RING domain is the binding determinant. RNF2 showed a ubiquitin ligase (E3) activity in the presence of Hip‐2, suggesting that a subset of RING finger proteins may have roles as E3s.