Size heterogeneity of the structural units of brain nuclear ribonucleoprotein particles.

Nuclear ribonucleoprotein particles were examined by electron microscopy after negative staining. The results confirmed the polymeric nature of the particles. The constitutive units were distributed into 4 size classes (diameters varying from 100 to 300 A, approximately) indicating that the monoparticle population was heterogenous. When examined on ultrathin sections, the particles had a fibrillar appearance.