The matrix gene expression of subacute sclerosing panencephalitis (SSPE) virus (Osaka-1 strain): A comparison of two sibling viruses isolated from different lobes of an SSPE brain

The Fr/V and Oc/V sibling viruses of the Osaka-1 strain of the subacute scl erosing panencephalitis (SSPE) virus were defective in cell-free virus prod uction. By radioimmunoprecipitation assay, the matrix (M) protein was not d etected in cells persistently infected with the Osaka-1 strain. This undete ctable expression was consistent with the selective reduction of antibody r esponse to the M protein in the patient from whom the Osaka-1 strain was is olated. The sequence of the M gene, however, predicted that the protein cou ld be synthesized because the translational start and stop codons for the p rotein were not altered, Northern blot hybridization demonstrated the selec tive defect of the monocistronic mRNAs for the M protein and the phosphopro tein (P) together with the dominant presence of the P-M bicistronic mRNA, T his absence of the hi mRNA was further confirmed by primer extension analys is. Therefore, the undetectable expression of the M protein in the infected cells was proved to be caused by a transcriptional defect, The two sibling viruses, isolated from remote portions of an SSPE brain, were indistinguis hable in their viral characters, including the M gene sequences, which indi cates the possibility of clonal expansion of the strain in the brain.