How to get out: ssRNA enveloped viruses and membrane fission

• Some but not all enveloped viruses recruit the ESCRT machinery for release.
• ESCRT-III assembles into spiral dome-like structures that together with VPS4 may catalyze membrane fission.
• ESCRT-independent influenza virus employs an amphipathic helix from M2 to catalyze fission.
• Glycoproteins from enveloped viruses such as flaviviridae assemble into an exterior protein coat-like structure, which may contribute to fission.

Enveloped viruses acquire their membrane from the host cell and accordingly need to separate their envelope from cellular membranes via membrane fission. Although some of the enveloped viruses recruit the endosomal sorting complex required for transport (ESCRT) to catalyze the final fission reaction, many enveloped viruses seem to bud in an ESCRT-independent manner. Here we describe the principles that govern membrane fission reactions in general and review progress in the understanding of ESCRT-mediated membrane fission. We relate ESCRT function to budding of single stranded RNA viruses and discuss alternative ways to mediate membrane fission that may govern ESCRT-independent budding.

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