Number of transcribing RNA polymerase molecules and polyribonucleotide elongation rates in regenerating rat liver. Effect of cycloheximide treatment

Abstract

Increased labelling of UMP internal residues is more marked in form I — than in form II — promoted RNA synthesis by regenerating liver nuclei in vitro and only form I RNA polymerase seems to enhance labelling of uridine in the 3′-termini. Increase in the number of transcribing polymerase I molecules and of their elongation rate is responsible for the activation of RNA synthesis — which affects essentially pre-ribosomal RNA synthesis — in regenerating livers. Pre-treatment of the rats with cycloheximide, at a dose which suppresses protein synthesis but not RNA synthesis in normal rats, prevents both effects and therefore the increase in RNA synthesis in regenerating liver.