Measles virus persistent infection: modification of the virus nucleocapsid protein.

The synthesis of intracellular measles virus proteins in persistently infected human cell cultures was studied. The virus-induced proteins were analysed after radioimmunoprecipitation by one- and two-dimensional polyacrylamide gel electrophoresis. The measles virus-induced nucleoprotein (NP) synthesized in persistently infected cells had a reduced binding capacity with measles virus antibodies (human convalescent serum) compared to the NP protein induced by the virus used to initiate the infection. In contrast, monospecific rabbit serum prepared against the original virus NP, or monoclonal anti-NP antibodies, precipitated NP proteins from acutely and persistently infected cells with equal efficiency. When the NP in acutely or persistently infected cells was labelled with either 14C- or 3H-amino acids and subjected to two-dimensional gel analysis, significant charge differences were observed between the virus proteins. When measles virus-infected cells were examined for virus protein synthesis at 40 degrees C, although no change was found in acutely infected cells, NP was not detected in the persistent infection.