Molecular analysis of virus-producing and non-producing clones derived from a defective SSPE virus Yamagata-1 strain

Two virus clones were isolated from a defective SSPE virus, the Yamagata-1 strain, and designated as the YA and YF clones. The YA clone-infected cells produced neither cell-free virus nor cell-associated virus, whereas the YF clone-infected cells produced both cell-associated and cell-free virus. No difference of epitopes on structural proteins was observed between these two clones. Both clones had hemadsorption activity. Quantitation of structural protein by Western dot blots showed relatively a lower amount of M protein in the YA-infected cells than that in the YF-infected cells. The ratio, P plus M dicistronic/M monocistronic mRNA, in the YA-infected cells was about twice that in the YF-infected cells. Sequence analysis of cDNA corresponding to P plus M dicistronic mRNA revealed that the deduced M protein of the YF virus was smaller than that of the YA virus by five amino acids from the carboxy terminal. These results suggest that abundant production of P plus M dicistronic mRNA is responsible for the reduced amount of M protein in the non-productive YA clone.