The Ub Proteasome Pathway (UPP) is the principal mechanism for protein catabolism in the mammalian cytosol and nucleus. In order to enhance the Ub-mediated degradation efficiency of M protein, we expressed a Ub-M fusion protein in BHK-21 cells using the eukaryotic expression plasmid pVAX1-Ub-M, in which the Ub coding sequence was fused in-frame with the PRRSV M coding sequence. Following transient transfection of BHK-21 cells with the pVAX1-Ub-M plasmid, the Ub-M fusion protein was expressed and accumulated predominantly in the cytoplasm (Additional file 2, Fig. S2 ).