Modification of nonstructural protein 1 of influenza A virus by SUMO1.

Nonstructural protein 1 (NS1) is one of the major factors resulting in the efficient infection rate and high level of virulence of influenza A virus. Although consisting of only approximately 230 amino acids, NS1 has the ability to interfere with several systems of the host viral defense. In the present study, we demonstrate that NS1 of the highly pathogenic avian influenza A/Duck/Hubei/L-1/2004 (H5N1) virus interacts with human Ubc9, which is the E2 conjugating enzyme for sumoylation, and we show that SUMO1 is conjugated to H5N1 NS1 in both transfected and infected cells.

Influenza A virus replication induces cell cycle arrest in G0/G1 phase.

Many viruses interact with the host cell division cycle to favor their own growth. In this study, we examined the ability of influenza A virus to manipulate cell cycle progression. Our results show that influenza A virus A/WSN/33 (H1N1) replication results in G(0)/G(1)-phase accumulation of infected cells and that this accumulation is caused by the prevention of cell cycle entry from G(0)/G(1) phase into S phase.

Intracellular distribution of NS1 correlates with the infectivity and interferon antagonism of an avian influenza virus (H7N1).

Highly pathogenic avian influenza viruses of subtype H7N1 that emerged during an outbreak in 1999 and 2000 in Italy differ from their low-pathogenicity precursor viruses by changes in several genes, including three mutations in the NS1 protein. Two of them involve amino acid exchanges located within or closely adjacent to the nuclear export signal of NS1. The third mutation resulted in a new stop codon and thereby a C-terminal truncation of the NS1 protein of the highly pathogenic viruses.

Mutations at positions 186 and 194 in the HA gene of the 2009 H1N1 pandemic influenza virus improve replication in cell culture and eggs.

Obtaining suitable seed viruses for influenza vaccines poses a challenge for public health authorities and manufacturers. We used reverse genetics to generate vaccine seed-compatible viruses from the 2009 pandemic swine-origin influenza virus. Comparison of viruses recovered with variations in residues 186 and 194 (based on the H3 numbering system) of the viral hemagglutinin showed that these viruses differed with respect to their ability to grow in eggs and cultured cells.

Human RNA polymerase I-driven reverse genetics for influenza a virus in canine cells.

We have established a human RNA polymerase I (pol I)-driven influenza virus reverse genetics (RG) system in the Madin-Darby canine kidney 33016-PF cell line, which is approved for influenza vaccine manufacture. RNA pol I polymerases are generally active only in cells of species closely related to the species of origin of the polymerases. Nevertheless, we show that a nonendogenous RNA pol I promoter drives efficient rescue of influenza A viruses in a canine cell line.