FIG 1.

Nascent influenza virus virions observed on a membrane sheet. A planar sheet of plasma membrane was prepared from CV1 cells infected with influenza virus A/WSN/33. WSN buds as spherical particles identifiable by electron-dense vRNP cores (red circles). Putative budozones with budding virions were seen as areas of high electron density (examples are in blue boxes). The cytoplasmic face of the membrane is oriented face up; frequently, the viral glycoprotein surface spikes were discernible despite viruses being viewed through the membrane sheet (inset, yellow arrows). Bar, 200 nm.