The importance of protein ratios for VLP formation was alluded to in a previous NDV study where the expression plasmids were co-transfected at ''pre-determined concentrations'' to produce VLP-incorporated protein ratios analogous to those in virus infected cells [49] . In a study by Patch el al [48] , equivalent amounts of NiV N, M, F and G were initially used to produce the VLPs. In that study, VLPs were subsequently also made by adjusting NiV expression plasmid concentrations by experimental variations similarly to that in the NDV study [49] . The efficiency of particle formation and budding in both these, and many other paramyxovirus VLP formation systems was based on M protein release [43, 44, 45, 46, 48] .