Rapid enhancement of chick intestinal DNA dependent RNA polymerase II activity by 1α,25 dihydroxyvitamin D₃, in vivo

1α,25 dihydroxy colecalciferol was examined for its ability to affect the DNA-dependent RNA polymerases (nucleoside triphosphate : RNA nucleotidyltransferase, EC 2.7.7.6) of rachitic chick intestinal cell nuclei in vivo. Nucleoplasmic (form II) RNA polymerase activity was stimulated 2 fold (P<0.05) within 2 to 3 hr after oral dose of 0.27 μg (0.65 nmol) of 1α,25 dihydroxy colecalciferol to rachitic chicks. The form II polymerase activity returned to control values by 5 to 9 hr after dosing with the sterol. In contrast, the nucleolar (form I) RNA polymerase was not increased within this period. Solubilization of nuclear protein and resolution of the 2 RNA polymerases on DEAE-Sephadex also revealed that there was an increase in polymerase II activity when assayed on exogenous DNA template. This evidence suggests that 1α,25 dihydroxy colecalciferol acts at the level of the enzymology of intestinal cell transcription and that increased mRNA synthesis after administration of this hormone cannot be due solely to a change in chromatin template activity.