Native morphology of influenza virions

Abstract

Influenza A virus is an enveloped virus with a segmented, single-strand, negative-sense RNA genome. Its virions show spherical or filamentous shapes of about 100 nm in diameter and occasionally irregular morphology, which exemplifies the pleomorphic nature of these virions. Each viral RNA segment forms a ribonucleoprotein complex (RNP), along with an RNA-dependent RNA polymerase complex and multiple copies of nucleoproteins; the RNPs reside in the enveloped virions. Here, we focus on electron microscopic analyses of influenza virions and RNPs. Based on the morphological and structural observations obtained by using electron microscopic techniques, we present a model of the native morphology of the influenza virion.

Keywords: electron microscopy; influenza virus; morphology.

Figure 1

Electron micrograph of influenza virions. The virions were purified by ultracentrifugation, and visualized by negative-staining EM. Bars, 200 nm. (A) Spherical virions [A/WSN/33 (H1N1)], (B) filamentous virions [A/Udorn/307/72 (H3N2)], and (C) irregular-shaped virions [A/Puerto Rico/8/34 (H1N1)].

Figure 2

Schematic diagram of influenza virions. Left, an elliptical virion; right, a filamentous virion. Note that both virions contain an organized set of eight RNPs at the end of the virion.