Studies on informational RNAs and ribonucleoproteins of normal rat liver, Zajdela hepatoma and liver of hepatoma-bearing rats

DNA-like RNA (D-RNA) species, both as constituents of RNP particles and protein-free molecules, isolated from normal rat liver, Zajdela ascites hepatoma and liver of tumor-bearing animals were compared with respect to their sedimentation and chromatographic behaviour. A selective labelling of D-RNA was carried out under actinomycin D-induced block of rRNA synthesis. No detectable differences in nuclear D-RNAs of the tissues compared could be observed whereas cytoplasmic D-RNAs of hepatoma and liver of tumor-bearing rats appear to be much more heterogeneous as compared to those of normal liver. The kinetics of the labelled D-RNAs appearing in the cytoplasm in case of malignant cells also differs from that characteristic of normal liver cells. The comparative analysis of cytoplasmic RNP complexes in the sucrose density and CsCl isopycnic band centrifugation revealed a shift in the ratio of polyribosome-bound and free complexes in favour of the latter in the tumor and liver of tumor-bearing rat as compared with normal liver. The data presented are interpreted to indicate a certain impairment in the selective nucleus-to-cytoplasm transport of RNA in tumor cells, the cells of tumor-bearing animal occupying in this respect an intermediate position between normal and tumor tissues.