The influenza B virus BM2 protein may be involved in the ribonucleoprotein complexes through the binding with membrane protein M1

Abstract

Background: The influenza B virus genome RNA segment 7 encodes M1 and BM2 proteins. We have shown previously that in virus-infected MDCK cells, the BM2 is synthesized as a cytoplasmic product, and thereafter, transported from the outside of the nuclear membrane to the virion budding site on the plasma membrane, resulting in the incorporation into virion. Methods: The interactions of virus proteins were analyzed by immunoprecipitation, mammalian two-hybrid system and indirect immunofluorescence. Results: By two-hybrid analysis, the BM2 was shown to interact with the M1 and the nuclear export protein NS2, but not with NP. Fractionation of viral ribonucleoprotein (vRNP) complexes extracted from the cytoplasm of infected cells indicated that the BM2 was detected in the vRNP complexes containing M1, but not in the M1-free vRNP complexes. Moreover, the localization of BM2 in the cytoplasm was highly correlated with that of vRNP complexes in the late phase of infection. Conclusion: The BM2 protein might be involved in vRNP complexes through binding with M1 protein, which is a component of vRNP complex.