MEMBRANE-PROTEIN LATERAL INTERACTIONS CONTROL SEMLIKI FOREST VIRUS BUDDING

Semliki Forest virus, SFV, directs the synthesis of two membrane prote ins, p62 and E1, which form a p62E1 heterodimer in the endoplasmic ret iculum. After being transported to the plasma membrane (PM), they are incorporated into the virus membrane during the process of virus buddi ng. Electronmicroscopic analyses of the envelope in matured virus show that the heterodimers are clustered into trimeric structures (spikes) which further form a regular surface lattice with T = 4. In this work we have used a genetic approach to study the importance of the trimer ization event for virus budding. We have coexpressed a budding compete nt form of the virus heterodimer with another one which cannot be used for particle formation because of a defect in nucleocapsid (NC) bindi ng. We show that the NC binding-deficient heterodimer is able to inhib it the budding of the competent one in a concentration-dependent manne r and that the NC binding-competent heterodimers can rescue the incomp etent ones into virus particles. This suggests that the heterodimers a re complexed together, probably into the trimeric structures (spikes), at the PM to expose a multivalent binding site for the NC and thereby drive efficient virus budding.