Macromolecular requirements for abrogation of Fv-1 restriction by murine leukemia viruses

Abstract

The molecular basis of abrogation of Fv-1 restriction in mouse cells by murine leukemia virus was investigated. Two different lines of experimentation indicated that high-molecular-weight viral RNA is required for abrogation. First, the decay of abrogating ability of virus stocks heated at 43 degrees C was quantitatively correlated with a loss of intact virion 35S RNA. Second, Act D virions, which lack such RNA although they contain normal structural proteins, failed to abrogate. These findings imply that abrogation does not result from the mere entry of virion structural proteins into a cell. Additional data indicate that the role of viral RNA in abrogation is not that of a template for DNA synthesis. Virus particles lacking reverse transcriptase activity as a result of either mutation or heat inactivation exhibit abrogating activity even though they do not synthesize detectable viral DNA. In addition, abrogation was shown to take place in the presence of cytosine arabinoside, an inhibitor of DNA synthesis. Thus, abrogation does not depend on viral or cellular DNA synthesis, and the role of viral RNA in this process must involve some other function. The nature of this viral function and its occurrence in Fv-1 permissive cells are discussed.

Abrogation of Fv-1 restriction by genome-deficient virions produced by a retrovirus packaging cell line

“…A specific role for virion RNA is apparently not required. This is in contrast to the model proposed by Bassin et al (1,2). That model was based on several observations, including the finding that abrogation did not require reverse transcription, and loss of abrogating activity at 43°C was correlated with loss of intact 35S RNA.-However, the ability of core particles to bind the Fv-1 gene product may require a structural integrity that parallels the stability of genomic RNA.…”

“…In that regard, the genome-deficient (replication-defective) virions produced by the packaging cell lines might be expected to be capable of abrogation. Although the ability to replicate is not required for abrogation, the model proposed by Bassin et al (1,2) implicated virion RNA in the abrogation mechanism. According to that model, virions lacking MuLV-specific coding sequences would be unable to abrogate.…”

“…A subsequently encountered virus is therefore able to replicate without interference. The abrogating virus must be of the restricted tropism, but does not have to be able to replicate (e.g., it may be heat inactivated) (1,2).…”