[Poly-A-containing RNA from the spleens of mice infected with Rauscher leukemia virus]

A fraction of RNA (RNA-x) which is eluted by distilled water from cellulose columns upon alcohol fractionation has been isolated from spleens of BALB/c mice, both normal and infected with Rauscher virus. RNA-x has sedimentation constant 15--16S and upon fractionation on cellulose columns in media of high ionic strength is eluted by water. This RNA is retained on nitrocellulose filters both before and after treatment with RNA-ase. The poly-A fragment resistant to RNA-ase is heterogenous in sucrose gradient, with the main peak in the zone of 3S. RNA-x localizes in polysomes and has not been found in mitochondria. In a cell-free protein-synthesizing system RNA-x stimulated incorporation of amino acids into the acid-insoluble fraction.