= Viral budding
<Viral budding> is a mode of particle assembly and release in which a host membrane curves around viral components and becomes the <viral envelope> of a departing <virion>. It connects the assembly of internal viral structures to organization of the membrane at the release site. The envelope is consequently derived from a particular cellular membrane region, rather than added later as an unrelated coat.<Asymmetric budding of viruses in epithelial monlayers: a model system for study of epithelial polarity by E. Rodriguez Boulan and D. D. Sabatini>[Abstract, membrane acquisition during budding]{ref}
A 1978 experiment used polarized <epithelial cells> grown as monolayers. Influenza particles budded from the apical surface, while <vesicular stomatitis virus> acquired its envelope from the basolateral surface. Those contrasting locations within the same type of cell made viral release a probe of membrane organization.<Asymmetric budding of viruses in epithelial monlayers: a model system for study of epithelial polarity by E. Rodriguez Boulan and D. D. Sabatini>[Abstract, apical/basolateral contrast]{ref}
The example separates three measurable events: producing viral components, assembling a particle and releasing it at a particular surface. More components inside a <biological cell> do not automatically demonstrate more released virions. Likewise, a change in release location need not mean that the viral genome changed. Structural and molecular measurements must be connected to the particular step being tested.
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