Electron microscopic observations on the poly(A)-RNP component of the pre-mRNA containing nuclear complexes

The nuclear ribonucleoprotein particles containing polyadenylic acid were prepared from rat liver nuclear extract by treatment with RNase I. The sedimentation coefficient of the particles was approximately 14 S. These particles represent a component of the pre-mRNA containing ribonucleoprotein complexes of the nucleus. The submicroscopic morphology of the particles was examined in preparations pretreated by platinum-palladium shadowing and by various negative staining methods as well as in ultrathin sections. The 14 S particles are globular structures, 120-140 A in diameter. The particles are characterized by a strong tendency to aggregation. The results are discussed with respect to mRNA transport.