Histones as a target for influenza virus matrix protein M1.

Matrix protein M1 purified from influenza A and B viruses has been analyzed for its ability to specifically interact with cellular proteins by immune coprecipitation and by an in vitro binding assay on nitrocellulose on PVDF membranes. When M1 was mixed with lysates of uninfected cells there was selective binding of histones H2A, H2B, H3, and H4. Week binding of H1 was also observed. The binding specificity of M1 was confirmed by using purified histones. The M1-histone complexes were dependent on pH and ionic strength, indicating electrostatic interactions. Chemical cleavage of M1 by formic acid into an N-terminal 9-kDa fragment and a C-terminal 18-kDa fragment did not abolish interaction with histones. However, after treatment with 1 M sodium chloride cleaved M1 no longer bound to histones, whereas uncleaved M1 showed an increased binding activity after salt treatment. These findings suggest that both N- and C-terminal domains of M1 are involved in histone binding and that conformation of M is an important factor in this interaction. The data support the notion that there is specific interaction of M1 with nucleosomes during the nuclear phase of influenza virus replication.