Physical and biochemical properties of progressive pneumonia virus.

The physical and biochemical characteristics of progressive pneumonia virus were found to be remarkably similar to those of the ribonucleic acid (RNA) tumor viruses. Significant findings included the presence of a 60 to 70S RNA genome, RNA-dependent deoxyribonucleic acid polymerase activity, and common morphological properties. This information correlates with previously reported biological observations and supports the provisional inclusion of enveloped RNA-containing "slow viruses" within the RNA tumor virus group.