Figure 1 (Left) Diagram of an Influenza A virus virion in section. The indicated glycoproteins embedded in the lipid membrane are the trimeric hemagglutinin (HA) which predominates and the tetrameric neuraminidase (NA). The envelope also contains a small number of M2 membrane ion channel proteins (not shown on diagram). The internal components are the M1 membrane (matrix) protein and the viral ribonucleoprotein (RNP) consisting of RNA segments, associated nucleocapsid protein, NP, and the PA, PB1 and PB2 polymerase proteins. (Right) Negative contrast electron micrograph of 3 particles of Influenza A virus (FLUAV). The bar represents 100 nm.
Figure 2 Orthomyxovirus genome organization. The genomic organization and ORFs are shown for genes that encode multiple proteins. Segments encoding the polymerase, hemagglutinin, and nucleoprotein genes are not depicted as each encodes a single protein. (A) Influenza A virus segment 8 showing NS1 and NS2 mRNAs and their coding regions. NS1 and NS2 share 10 amino-terminal residues, including the initiating methionine. The ORF of NS2 mRNA (nts 529-861) differs from that of NS1. (B) Influenza A virus segment 7 showing M1 and M2 mRNAs and mRNA3 and their coding regions. M1 and M2 share 9 amino-terminal residues, including the initiating methionine; however, the ORF of M2 mRNA (nts 740-1004) differs from that of M1. A peptide that could be translated from mRNA3 has not been found in vivo. (C) Influenza B virus RNA segment 7 ORFs and the organization of the ORFs used to translate the M1 and BM2 proteins. The stop-start pentanucleotide is also illustrated. (D) Influenza C virus mRNAs derived from RNA segment 6 and the CM2 coding region (third line). (E) ORFs in Influenza B virus RNA segment 6, illustrating the overlapping reading frames of NB and NA. Nucleotide sequence surrounding the 2 AUG initiation codons, in the mRNA sense, is shown. Dark lines at the 5- and 3-termini of the mRNAs represent untranslated regions. The boxes represent different coding regions. Introns in the mRNAs are shown by the V-shaped lines; filled rectangles at the 5-ends of mRNAs represent heterogeneous nucleotides derived from cellular RNAs that are covalently linked to viral sequences. (From Cox and Kawaoka, 1998 modified from Lamb and Horvath 1991.)
Figure 3 Phylogenetic relationships within the family Orthomyxoviridae and comparison with the Human parainfluenza virus 2 (Courtesy of Michael Shaw). NP gene sequences were aligned, corrected for multiple substitutions, and bootstrapped 1000 times using the Clustal W Multiple Alignment Program (Thompson, Higgins and Gibson, 1994). The unrooted phylogenetic tree was constructed from the calculated sequence differences using the Phylogenetic Inference Package (Phylip 3.5C; Felsenstein, 1989), with the sequence of Human parainfluenza virus 2 (HPIV-2) as an outliner. The bootstrap values are indicated on the branches. The GenBank accession numbers for the sequences used for comparison were (top to bottom) X57559, M17435, X96872, M17700, AF005739, M20174, K001139, X14217, K01395, J02137, L07354, D00601, D00603, M63752, M30760, M63757, and M57559.
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