A Single Herpesvirus Protein can mediate Vesicle Formation in the Nuclear Envelope

Herpesviruses assemble capsids in the nucleus and egress by unconventional vesicle-mediated trafficking through the nuclear envelope. Capsids bud at the inner nuclear membrane into the nuclear envelope lumen. The resulting intralumenal vesicles fuse with the outer nuclear membrane delivering the capsids to the cytoplasm. Two viral proteins are required for vesicle formation, the tail-anchored pUL34 and its soluble interactor pUL31. Whether cellular proteins are involved is unclear. Using giant unilamellar vesicles we show that pUL31 and pUL34 are sufficient for membrane budding and scission. pUL34 function can be by-passed by membrane-tethering of pUL31 demonstrating that pUL34 is required for pUL31 membrane recruitment but not for membrane remodelling. pUL31 can inwardly deform membranes by oligomerizing on their inner surface to form buds which constrict to vesicles. Thus a single viral protein can mediate all events necessary for membrane budding and abscission.