Figure 5: A non-proteolytic function for ubiquitin in the regulation of mRNA decay.

(a) Neither proteasome nor lysosome inhibitors rescue MEX-3C-mediated degradation of FF-Luc-HLA-A2-3′UTR mRNA in-vivo. CcmA, Concanamycin A. FF-Luc-HLA-A2-3′UTR mRNA levels were analysed as in Fig. 2. Results are expressed as mean±s.d. of three independent experiments and relative to empty vector control. (b,c) Ubiquitin lysine mutants are unable to rescue MEX-3C-mediated downregulation of HLA-A2 protein levels (b, as determined by flow cytometry analysis) or luciferase protein levels from FF-Luc-HLA-A2-3′UTR reporter (c, as determined by relative luciferase activity). ‘b’ also serves as a control for the ubiquitin mutant (GFP) expression levels for the following experiments. (d) MEX-3C-mediated degradation of FF-Luc-HLA-A2-3′UTR reporter mRNA is rescued by K6R and K63R ubiquitin mutants. *P<0.05 and **P<0.005, both versus+MEX-3C+WT Ubiquitin treatment. NS, not significant; unpaired Student’s t-test. Results for this figure are expressed as mean±s.d. of three independent experiments and relative to empty vector control/GFP.