The appearance of new polyadenylated nuclear RNA sequences during rat-liver regeneration

Polyadenylated RNA populations from normal and 16-hour regenerating rat-liver nuclei were compared by heterologous hybridisation reactions with cDNA and unique DNA probes. Whereas unique DNA hybridisations did not show differences between the RNA populations, comparisons by cDNA hybridisation showed that about 10–15% by weight of polyadenylated sequences present in the nuclei of 16-hour regenerating rat livers were not found in the poly-adenylated nuclear RNA of normal rat livers. These regenerating-sepecific nuclear cDNA sequences were isolated and characterised; the experiments showed that the complexity of the new sequences was 1–2 x 107 nucleotides (equivalent to 5,000–10,000 RNA sequences of 2,000 nucleotides in length) and that they were probably not potential messenger RNA sequences.