Evidence for a cytoplasmic factor regulating murine leukemia virus DNA synthesis and its preliminary characterization

Abstract

Postmitochondrial cytoplasmic extracts, prepared from uninfected NIH/3T3 cells as well as from chronically or exogenously infected with murine leukemia virus (MLV), were found to stimulate the endogenous reaction of purified MLV reverse transcriptase. No such stimulation was observed with the exogenous reaction of this enzyme, using poly (rA) oligo (dT) as an exogenous template-primer. While the stimulatory capacity of extracts from uninfected and chronically infected cells was comparable, that of the exogenously infected cells was much more powerful in this respect. The stimulatory activity could be destroyed by trypsin, indicating that it was excerted by a protein. In uninfected and chronically infected cells this protein was found to be of a short functional life time under conditions blocking continuous protein synthesis. However the mRNA coding for this factor was found in these cells to be stable. On the other hand, the increased stimulatory activity, observed in extract of exogenously infected cells, was independent on protein synthesis and therefore was attributed to a protein apparently introduced into the cells by the penetrating virions. Experiments with monospecific antibodies against MLV proteins suggested that p30 is an important accessory for reverse transcriptase activity and that the cytoplasmic stimulatory factor might be also related to p 30.

Effect of interferon on the penetration of murine leukemia virus and the binding of its genome RNA to polyribosomes at the early stage of infection

“…However it cannot exclude the possibility that such a protein is required as an accessory for the in rive synthesis of the provirus DNA by viral reverse transcriptase. Preliminary indications for the existence of such an accessory and its relation to viral proteins have been presented in our recent study (1). In the present study we found that IFN treatment delayed the maximal binding of parental viral RNA to polyribosomes by 2 hours.…”