Investigation of the auto-ubiquitination and ubiquitination potentials of Retinoblastoma binding protein 6 and its binding to p53
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Retinoblastoma Binding Protein 6 (RBBP6) is a 200 kDa human protein known to play an essential role in mRNA 3’-end processing, as well as functioning as an E3 ligase to catalyze ubiquitination and suppression of p53 and other cancer-associated proteins. A RBBP6 knockout mouse model previously suggested that RBBP6 cooperates with MDM2 in polyubiquitinating p53, but is not able to ubiquitinate p53 without the assistance of MDM2. However, unpublished studies from our laboratory suggest that the N-terminal 335 residues of RBBP6, known as R3, are able to ubiquitinate p53 in full in vitro assays, and that the isolated RING finger of RBBP6 is able to catalyse ubiquitination of itself, a phenomenon known as auto-ubiquitination. It is, however, possible that other domains within RBBP6, in particular the ubiquitin-like DWNN domain situated near to the RING finger, may modulate the autoubiquitination and substrate-ubiquitination potentials of the complete protein.