Rapid metabolism of moloney leukemia virus precursor polypeptides in virus infected Swiss mouse embryo cells

The pathophysiology of murine retrovirus-induced leukemias

Murine leukemia viruses (MuLVs) are retroviruses which induce a broad spectrum of hematopoietic malignancies. In contrast to the acutely transforming retroviruses, MuLVs do not contain transduced cellular genes, or oncogenes. Nonetheless, MuLVs can cause leukemias quickly (4 to 6 weeks) and efficiently (up to 100% incidence) in susceptible strains of mice. The molecular basis of MuLV-induced leukemia is not clear. However, the contribution of individual viral genes to leukemogenesis can be assayed by creating novel viruses in vitro using recombinant DNA techniques. These genetically engineered viruses are tested in vivo for their ability to cause leukemia. Leukemogenic MuLVs possess genetic sequences which are not found in nonleukemogenic viruses. These sequences control the histologic type, incidence, and latency of disease induced by individual MuL Vs.

Isolation and characterization of DNA-binding proteins of Yoshida ascites tumour cells

DNA-binding proteins from the cytosol and nuclei of Yoshida ascites sarcoma cells were isolated by affinity chromatography on native and denatured DNA-cellulose columns. The proteins that were retained in the columns were eluted by increasing concentrations of NaCl and analysed by electrophoresis in polyacrylamide gels. Two proteins with approximate molecular weights (MW) of 38 000 (38K) and 34 000 (34K) D showed high affinity for denatured DNA and eluted in large quantities from denatured DNA-cellulose columns. In contrast, only small amounts of 38 000 and 34 000 D proteins were found to be associated with native DNA and the native DNA-associated 38K and 34K proteins showed higher rate of phosphorylation than the corresponding denatured DNA-binding proteins. The 38 000 and 34 000 D DNA-binding proteins were present both in nuclei and cytoplasm. These two proteins together comprised over 70% of the total DNA-binding proteins present in the 0.4 M NaCl eluate of the cytoplasmic extracts. DNA-binding proteins of MW 38 000 and 34 000 D were also present in a methylcholanthrene-induced fibrosarcoma, although in smaller amounts.

Sequence-specific antibodies show that maturation of Moloney leukemia virus envelope polyprotein involves removal of a COOH-terminal peptide

We followed maturation of the glycosylated envelope polyprotein Pr80env of a murine retrovirus by using antisera specific to subregions of the protein, including an antiserum directed against a synthetic peptide corresponding to the COOH-terminus of Pr80env. Shortly after synthesis and glycosylation, Pr80env is cleaved into two species, gp70 and Pr15E, that are found associated, perhaps through disulfide bonds, in infected cells. Pr15E is further cleaved at the time of virus maturation to form virus protein p15E. NH2-Terminal protein sequence analysis showed that Pr15E had an NH2 terminus in common with p15E. Pr15E, but not p15E, is precipitated by antibody against the COOH-terminal peptide; hence, p15E is missing a peptide at the COOH-terminus. Our data indicate that Pr15E is the predominant species in cells and p15E is the major species in virus.