Characterization of Messenger Ribonucleoprotein and Messenger RNA from KB Cells

Messenger ribonucleoprotein and mRNA from KB-cells were isolated under conditions designed to minimize nonspecific RNA-protein interaction and to minimize degradation by contaminating ribonucleases. A large fraction, 60-70%, of the messenger ribonucleoprotein from polysomes dissociated in vitro by either EDTA or puromycin sedimented faster than the large ribosome subunit. Messenger ribonucleoprotein particles with sedimentation coefficients up to 200 S were observed. Released mRNA was also large, with maximal molecular weights around 5 x 10(6).