Characterization and Partial Purification of Heterodisperse Polysomal RNAs in Normal and Neoplastic Cells
The size distribution of cytoplasmic messenger RNAs (m-RNA) has been studied in rat liver and in monodifferentiated cells (mouse reticulocytes and myelomas). It has been found that the RNA which exhibits a « rapid turnover » and a polydisperse profile of radioactivity is refractory to phenol extraction. This property has been exploited to selectively isolate m–RNA from the phenol residue by means of an extraction at an alkaline pH. The sucrose density gradient profiles of m–RNA isolated from monodifferentiated cells show monodisperse peaks having the sedimentation coefficients expected on the basis of the molecular weights of monocistronic messages for α and β chains of hemoglobin (reticulocytes) and L and H chains of immunoglobulin (myelomas). The sedimentation profile of cytoplasmic m–RNA associated with rat liver polysomes shows a much broader distribution, with sedimentation coefficients ranging from 8 S to 28 S.