Biochemical properties of endogenous rat C-type viruses

Area of Science:

• Virology
• Molecular Biology
• Oncology

Background:

• Inducible C-type viruses in rats face cellular restrictions to persistence.
• Rat leukemia viruses (RaLV), including SD-RaLV and W-RaLV, are C-type oncornaviruses.
• These viruses share characteristics with known oncornaviruses, such as buoyant density and RNA content.

Purpose of the Study:

• To investigate the overcoming of cellular restrictions for rat C-type virus persistence.
• To characterize the biochemical properties of SD-RaLV and W-RaLV.
• To determine the endogenous or exogenous nature of these rat viruses and their role in cell transformation.

Main Methods:

• In vitro replication and spontaneous transformation assays of rat embryo cells.
• Morphological and biochemical analysis of viral particles.
• Buoyant density determination using sucrose gradients.
• Assay of viral DNA polymerase activity with varying metal ion concentrations.
• Molecular hybridization and competition hybridization assays to determine proviral sequence copy number.

Main Results:

• Cellular restrictions to SD-RaLV and W-RaLV persistence were overcome in replicating/transforming rat embryo cells.
• SD-RaLV and W-RaLV are C-type oncornaviruses with a buoyant density of 1.15 g/cm3 and high-molecular-weight RNA.
• The RaLV-associated DNA polymerase showed Mn++ preference and both exogenous and endogenous reactivity.
• Molecular hybridization confirmed the endogenous nature of SD-RaLV and W-RaLV.
• Competition hybridization indicated 84 proviral sequences per haploid cell genome.

Conclusions:

• The study demonstrates that rat C-type viruses can persist in specific cellular environments.
• SD-RaLV and W-RaLV are endogenous retroviruses of rats.
• The findings suggest a potential role for these endogenous rat viruses in spontaneous in vitro cell transformation.