Reassortment of influenza A virus genes linked to PB1 polymerase gene

Influenza virus generates most new antigenic variants in two ways, either by antigenic drift of the Haemagglutinin (HA) and Neuraminidase (NA) or by antigenic shift involving genomic reassortment. Influenza pandemics like those that occurred in 1957 and 1968 are thought to have involved reassortment of HA and NA genes between human and avian or swine viruses. The factors controlling reassortment are not known. The aim of this study was to investigate an observed reassortment restriction between two influenza viruses. In numerous experiments no reassortants were found in mixed infections of A/USSR/90/77 (H1N1) and A/Shearwater/37/72 (H6N5). However, A/USSR/77 is known to have formed reassortants with human H3N2 strains in nature. In mixed infection experiments involving A/USSR/90/77, A/Shearwater/37/72, and a human H3N2 virus strain, an H6N1 reassortant was isolated. RNA-RNA hybridization and gene sequence analysis showed that the only gene segment transferred from the H3N2 parent to the H6N1 reassortant was the H3 PB1 polymerase segment. These results indicate that the PB1 (gene or polymerase) may be required for gene reassortment in influenza viruses. Crown Copyright (C) 2003 Published by Elsevier B.V. All rights reserved.