The Paramyxoviridae family includes several viruses that are important to human health, including measles virus. The envelope glycoproteins are essential for attachment and entry of the virus into the host cell [1, 2]. To develop novel therapeutics against the virus, detailed knowledge of envelope glycoprotein protein-protein interaction is important. The goal of this study is to characterize the MeV entry machinery on a molecular level. Interaction of haemaglutinin (H) and fusion (F) protein in pre-fusion form can be biochemically detected with DTSSP. To map the interaction site of H and F protein in pre-fusion form, we have mutated lysine (K) to arginine (R) in the F protein, and examined surface expression. The mutated F was still expressed on the surface and amount of surface expression correlated with fusion activity. The altered F proteins produced in this study will be used to further characterize the H-F interaction.