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RNA Tumour Virus Phosphorproteins: Evidence for Virus Specificity of Phosphorylation

Departments of Pathology and Biochemistry, University of Southern California School of Medicine, Los Angeles, California 90033, U.S.A.

The purified 12000 dalton (p12) phosphoprotein of Rauscher (R) and wild mouse (WM) strains of murine leukaemia virus (MuLV) was analysed for the distribution patterns of its variously charged molecular species by urea-poly-acrylamide gradient gel electrophoresis. The distribution patterns of the p12 of two different field isolates of WM viruses, 292 and 1504, and the mouse-tropic and amphotropic clonal sub-populations of 15-4 field isolate were very similar but different from that of MuLV-R. A unique characteristic of the p12 of the WM isolates is the presence of two major apparently non-phosphorylated species in approximately constant proportions relative to the phosphorylated species. Similar studies on the p12 of the same virus (MuLV-R or WM viruses) grown in different host cells showed that the patterns of phosphorylated and non-phosphorylated species are virus-specific and independent of the cell lines of propagation. These analyses and their comparison with urea-gel patterns of the phosphoproteins of other mammalian type C viruses indicated that the number and relative proportion of the variously phosphorylated and non-phosphorylated species are predetermined for a virus. Therefore, the virus must have the genetic information for the phosphoprotein as well as other necessary genetic information which functions, perhaps in conjunction with appropriate cellular factors, in regulating the specific proportions of these multiple species. Possible biological significance of the variously charged molecular species in the phosphoprotein of RNA tumour viruses is discussed.

Received 8 February 1977; accepted 19 April 1977.