Structural changes in influenza virus RNA during its attenuation

Changes in structures of only two genes of influenza virus--M and NS genes were found during virus attenuation by the method of oligonucleotide mapping. Such changes were observed in virulent and attenuated viruses (passages 10-23 in chick embryos) by comparing intermediate variants of the virus (passages 11-16 in chick embryos). These results allow us to conclude the important role of these genes in virus attenuation and in connection with virulence of the virus.