Isolation and characterization of free cytoplasmic messenger ribonucleoproteins from rabbit reticulocyte.

Free cytoplasmic messenger ribonucleoproteins have been prepared with a high yield in a zonal rotor. They are rapidly labelled by [3H]uridine. Their sedimentation coefficients are 14.6 S and 19.4 S. Their protein contents are higher than in ribosomes, as indicated by a shift towards greater wavelength in their ultraviolet spectra and a buoyant density of 1.39 g cm-2 in CsCl. They do not cross-react with antiribosome antibodies and their protein patterns in sodium dodecylsulfate and two-dimensional polyacrylamide gel electrophoresis are different from ribosomes'. They may contain up to 30 proteins. The proteins are acidic and their molecular weights range from 22 000 to 100 000. When compared to chromatin they behave more like non-histone proteins than histones.