Whilst the molecular details of interactions between virions and erythrocytes remain unknown it has been suggested that HA activity might be mediated by the trimeric E protein in its postfusion conformation rather than by native E dimers [32] . Five of these trimers form a fusion pore that enables fusion between the viral and cellular endosomal membrane thus releasing the viral RNA into the cellular cytoplasm. Therefore we mapped the chimaeric Yar-simulated mutants onto the crystal structure of the trimeric (post-fusion) conformation of the E protein [18] . This demonstrated that the 3 Yar-virus mutations are located along the most protruding parts of the lateral surface of the trimer (Fig. 2C ). Therefore they are likely to be able to make direct contact with the erythrocyte surface and/or with each other.