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Separation of a Murine Leukaemia Virus Protein Kinase Activity from its Pr65^gag Polyprotein Substrate After DNA-Cellulose Chromatography

Y. Yoshinaka

Department of Microbiology and Immunology, University of South Carolina School of Medicine, Columbia, South Carolina 29208, U.S.A.

We have recently found that, in vitro, the murine leukaemia virus (MuLV)-associated protein kinase activity predominantly phosphorylates Pr65^gag, a virus protein present in relatively small amounts in partially purified virus preparations. Other virus proteins, such as p10, Pr27^gag and Pr40^gag, are also phosphorylated in vitro, but to a lesser degree. Furthermore, when immature core subparticles which are enriched in Pr65^gag are prepared from virions by Sepharose 6B exclusion column chromatography, about 50% of the kinase activity (as assayed with the exogenous substrate phosvitin) remains associated with the cores. We report here that this core-associated activity is distinct from Pr65^gag since it can be separated from Pr65^gag by chromatography on denatured DNA-cellulose columns followed by centrifugation of the 0·2 M-NaCl-eluted fraction. Under these conditions, Pr65^gag is pelleted while the kinase activity, which can phosphorylate both endogenous (MuLV Pr65^gag and p10) as well as exogenous (phosvitin) substrates, remains in the supernatant. Interestingly, when the amount of Pr65^gag is reduced, as in such preparations, p10 then becomes more heavily phosphorylated.

Keywords: murine leukaemia virus, protein kinase, DNA-cellulose

Present address: Department of Microbiology, Mie University School of Medicine, 174 Edobashi-2-Chome, Tsu, Mie, Japan 514.

Received 25 January 1982; accepted 18 August 1982.