Changes in cellular concentration of DNA-dependent RNA polymerases A and B during regeneration of rat liver.

1. DNA-dependent RNA polymerases A and B were solubilized from rat liver nuclei at different intervals after partial hepatectomy, and chromatographed on DEAE-Sephadex A-25. Activity of the solubilized RNA polymerases remained unchanged till 6 h after hepatectomy, then started to increase reaching a maximum (350% and 150% of control for the A and B enzyme, respectively) at the 18th hour of regeneration, and was still high at the 36th hour of regeneration. 2. RNA polymerases A and B were extracted and extensively purified from the nuclei of normal and regenerating rat liver. No marked differences in the specific activities between the analogous purified enzymes from normal and regenerating liver were observed, thus the increase in RNA polymerase activities (especially marked in the case of enzyme A) observed after partial hepatectomy is probably due to a real increase in the quantities of enzymes. 3. Concentration of RNA polymerase A in hepatocyte increases from 1.3 x 10(4) (normal liver) to 7.5 x 10(4) (18 h after hepatectomy) molecules per haploid genome. The concentration of polymerase B increases from 3.4 x 10(4) to 5.5 x 10(4) molecules per haploid genome, respectively.