>Magister Scientiae - MSc / Retinoblastoma binding protein 6 (RBBP6) is a 250 kDa RING finger-containing protein whose function is known to be mediated through interaction with other proteins. RBBP6 plays a role in the regulation of the tumour suppressor protein p53 and is also thought to be involved in mRNA splicing although its role has yet to be characterised. A recent study utilising a yeast 2-hybrid screen identified the cancer-associated protein known as YB-l as an interacting partner of RBBP6, and showed that RBBP6 ubiquitinates YB-I, leading to its degradation in the
proteasome.Human Y-box binding protein 1 (YB-I) is member of the cold-shock domain family of proteins, which regulates a number of growth related genes through both transcriptional and translational mechanisms. YB-l is a cell-survival factor whose expression is increased in proliferating normal and cancer cells. It also protects cells against p53-mediated apoptosis by repressing the p53- promoter and down-regulating endogenous p53. The interaction between RBBP6 and YB-l involves the RING finger-like domain ofRBBP6 and the C-terminal62 amino acids ofYB-l. As a means of further localising the interaction, truncated fragments derived from the C-terminal region of YB-I, were tested for their interaction with the RING finger domain of RBBP6 using three different assays: a directed yeast 2-hybrid assay, co-immunoprecipitation and NMR chemical shift perturbation analysis. Our results suggest that the entire 62 amino acid region at the C-terminal domain ofYB-l may be involved in the interaction with RBBP6. Using chemical shift perturbation analysis, this study provides an indication of where YB-l binds to the RING fmger. This represents the first step towards the design of therapeutics aimed at modulating the
interaction between RBBP6 and YB-l as a means of targeting the oncogenic effects ofYB-l. In order to identify E2 enzymes involved in the ubiquitination of YB-I, we examined the efficiencies of selected E2s in an in vitro ubiquitination assay. UbcH5c and UbcH7 were both
found to catalyse the ubiquitination of YB-l in conjuction with RBBP6, whereas Ubc 13 was not. Finally, we show using NMR that two single-point mutations of the RING finger-like domain are sufficient to abolish homodimerisation of the domain. These will be used in future studies to investigate the requirement for homodimerisation on the ubiquitination activity of RBBP6.
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| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uwc/oai:etd.uwc.ac.za:11394/8802 |
| Date | January 2010 |
| Creators | Muleya, Victor |
| Contributors | Pugh, David J. R. |
| Publisher | University of the Western Cape |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Rights | University of the Western Cape |
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