The ribonucleoprotein particles from nuclear residual proteins of calf thymus

Abstract

Ribonucleoprotein particles have been isolated from calf thymus nuclear residual proteins prepared by combined NaCl extractions and DNase treatment. The residual nucleoprotein particles contain 91.3% protein, 7.4% RNA, and 1.3% DNA. The size range of the residual particles is 115–276 × 20–50 Å, and the average sedimentation coefficient, 33S. The residual particles contain a 5S RNA with a base composition similar to that of the nuclear ribosomes. The protein moiety of the residual particles is heterogeneous when examined by polyacrylamide gel electrophoresis. Chemical analyses of the residual particles show that the proteins have a high acidic amino acid content. Double labeling of the residual particles' proteins and RNA by incubation of isolated calf thymus nuclei with 3H-orotic acid and 14C-glutamic acid revealed a high metabolic activity of the residual RNA and low incorporation of labeled glutamic acid into protein. These properties are in contrast to those of the nuclear ribosomes.