Comparison of heterogeneous nuclear ribonucleoprotein particles of the developing rat liver.

hnRNP monoparticles were isolated from livers of newborn (1 day), 7, 10, 11, 14, 21, 28 days old and adult rats, and their sedimentation properties, buoyant densities and protein composition were compared. There were observable differences neither in sedimentation nor in buoyant density among the particles isolated from livers of rats of different ages. The hnRNP particles derived from every stage of ages sedimented in the 30-50S zone of sucrose gradient with a peak at about 38S. Glutaraldehyde fixed particles in CsCl gradients banded at 1.36 g/cm3 which corresponds to about 80% of protein in the particles. Urea/sodium dodecyl sulfate/polyacrylamide gel electrophoresis of hnRNP proteins demonstrated 19 polypeptides in the 35,000-140,000 Mr range. Three main polypeptides in hnRNP of every group of animals could be observed with apparent Mr of 39,000, 43,000 and 46,000. In the minor components only quantitative differences could be seen in the different age groups with the exception of a 35,000-Mr polypeptide which appeared on the 11th day after the birth.