Matrix protein of cell-associated subacute sclerosing panencephalitis viruses.

The nucleotide sequence has been determined for the matrix (M) protein gene of three strains, Niigata-1, ZH and Biken, of cell-associated subacute sclerosing panencephalitis (SSPE) virus. The M proteins of the Niigata-1 and ZH strains were found to terminate prematurely as a result of nonsense mutations at nucleotide positions 68 and 96 respectively. On the other hand it was predicted that the Biken strain would express M protein with 22 amino acid differences and eight additional amino acids at its C terminus in comparison to the M protein of the Edmonston strain of measles virus. Radiolabelling of cells carrying the Biken strain showed the production of an M protein with considerably altered immunoreactivity and a marked reduction in intracellular stability. Either premature termination or rapid degradation of the M protein may underlie the defectiveness of these three strains of SSPE virus.