Characterisation of S. pombe Dph1 and Rhp23 and their roles in targeting polyubiquitinylated substrates to the proteasome. (360G-Wellcome-080823_Z_06_Z)

The ubiquitin (Ub)-mediated protein degradation pathway regulates many critical eukaryotic cellular functions that include cell cycle control, protein quality control and transcription regulation. Four K48-linked Ub molecules attached to the target protein has been shown to be the minimal signal for degradation. Although the molecular interactions that mediate the selective recognition of Lys48-linked polyUb chains by particular Ub-interacting domains (UBAs) have been elaborated, our recent structural studies have also shown that alternative models may exist. These observations suggest that UBA domain containing proteins may employ diverse mechanisms for Ub recognition that may be an intrinsic property of the isolated UBA domain but may also be dependent on its protein environment. Once the polyUb signal is recognised, a number of pathways have been characterised that deliver polyubiquitinylated substrates to the proteasome. However, it is still unclear whether once at the proteasome all proteasome substrates are processed through the same pathway or whether multiple parallel and/or alternative pathways exist. This project aims to (i) Elaborate the interactions between Dph1 and Rhp23, (two proteins that contain both a Ub-like domain (UBL) and a Ub-associating domain (UBA) and are proposed to act as shuttle proteins to bring polyubiquitinylated substrates to the proteasome) and Ub chains; (ii) characterise the interactions between Dph1 and Rhp23 with Mts4 (a subunit of the 19S proteasome lid sub-complex); and (iii) Elaborate the role of Pus1 as a facilitator of the interaction between Rhp23 and Mts4.