MORPHOLOGY
Virions are 100–430 nm in length and 45-100 nm in diameter. Defective virus particles are propor-
tionally shorter. Viruses infecting vertebrates are bullet-shaped or cone-shaped; viruses infecting
plants mostly appear bacilliform when fixed prior to negative staining; in unfixed preparations they
may appear bullet-shaped or pleomorphic. The outer surface of virions (except for the quasi-planar
end of bullet-shaped viruses) is covered with projections (peplomers) which are 5–10 nm long and
about 3 nm in diameter. They consist of trimers of the viral glycoprotein (G). A honeycomb pattern of
peplomers is observed on the surface of some viruses. Internally, the nucleocapsid, about 30–70 nm
in diameter, exhibits helical symmetry and can be seen as cross-striations (spacing 4.5–5 nm) in neg-
atively stained and thin-sectioned virions. The nucleocapsid consists of a ribonucleoprotein (RNP)
complex comprising the genomic RNA and tightly bound nucleoprotein (N) together with an
RNA-dependent RNA polymerase (L) and phosphoprotein (P). The RNP complex is active for tran-
scription and replication: the N-RNA template is processed by the L protein, which contains most
enzymatic activities, and its cofactor the P protein. In the cytoplasm, the RNP complex is uncoiled
and filamentous, about 700 nm in length and 20 nm in diameter (Figure 1). In the virion, the lipid
envelope containing the G protein interacts with the coiled RNP complex via the matrix protein (M).
MORPHOLOGY
Virions are 100–430 nm in length and 45-100 nm in diameter. Defective virus particles are propor-
tionally shorter. Viruses infecting vertebrates are bullet-shaped or cone-shaped; viruses infecting
plants mostly appear bacilliform when fixed prior to negative staining; in unfixed preparations they
may appear bullet-shaped or pleomorphic. The outer surface of virions (except for the quasi-planar
end of bullet-shaped viruses) is covered with projections (peplomers) which are 5–10 nm long and
about 3 nm in diameter. They consist of trimers of the viral glycoprotein (G). A honeycomb pattern of
peplomers is observed on the surface of some viruses. Internally, the nucleocapsid, about 30–70 nm
in diameter, exhibits helical symmetry and can be seen as cross-striations (spacing 4.5–5 nm) in neg-
atively stained and thin-sectioned virions. The nucleocapsid consists of a ribonucleoprotein (RNP)
complex comprising the genomic RNA and tightly bound nucleoprotein (N) together with an
RNA-dependent RNA polymerase (L) and phosphoprotein (P). The RNP complex is active for tran-
scription and replication: the N-RNA template is processed by the L protein, which contains most
enzymatic activities, and its cofactor the P protein. In the cytoplasm, the RNP complex is uncoiled
and filamentous, about 700 nm in length and 20 nm in diameter (Figure 1). In the virion, the lipid
envelope containing the G protein interacts with the coiled RNP complex via the matrix protein (M).
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