Notes on Genus: Influenzavirus B
enveloped spheres or pleomorphic
Type member: Influenza B virus
The genus Influenzavirus B
is one of the genera in the family Orthomyxoviridae
. It is named from the type (and only) member (derived from the latin influentia
= epidemic). Genome organisation is very similar to that for the genus Influenzavirus A
but there are large serological differences and a different organisation of RNA segment 6.
Virions spherical or pleomorphic, enveloped, 80-120 nm in diameter, with projections 4-6 nm in diameter and 10-14 nm long.
Single-stranded negative sense RNA in 8 segments totalling about 14.6 kb. The segments do not have a genome-linked protein (VPg) at their 5'-terminus nor a 3'-polyA tail.
Genus Genomic Organization
There are 8 RNA segments. The larger genome segments each encode a single protein while the smaller segments often encode additional proteins from spliced or bicistronic mRNAs.
Type Member Genomic Organization
There are 8 RNA segments:
- RNA1 (2368 nts) encodes a basic polymerase (PB1) of 84.4 kDa
- RNA2 (2396 nts) encodes a basic polymerase (PB2) of 87.9 kDa
- RNA3 (2308 nts) encodes an acid polymerase (PA) of 83.2 kDa
- RNA4 (1882 nts) encodes a hemagglutinin (HA) of 63.3 kDa
- RNA5 (1841 nts) encodes the coat protein (Nucleoprotein, NP) of 61.8 kDa
- RNA6 (1557 nts) encodes a neuraminidase (NA) of 51.4 kDa and a membrane protein (NB) of 11.0 kDa
- RNA7 (1191 nts) encodes two matrix proteins (M1 and M2) of 27.5 and 12.5 kDa
- RNA8 (1096 nts) encodes two non-structural proteins (NS1 and NS2) of 32.1 and 14.2 kDa