Hormonal regulation of transcription of rDNA: glucocorticoid effects upon initiation and elongation in vitro.
Various parameters of transcription of cloned mouse rDNA have been examined using extracts from control P1798 cells and from cells treated 24 h with 0.1 microM dexamethasone. Highly purified RNA polymerase I from either source catalyzes nucleotidyl transfer (elongation) at a rate of approximately 30 nucleotides/sec. Extracts from hormone-treated cells are capable of forming stable, preinitiation complexes. The rates of stable complex formation are the same in extracts from control and hormone-treated cells. Nevertheless, initiation of transcription does not occur in extracts from hormone-treated cells. Initiation in such extracts may be restored by the addition of a partially purified RNA polymerase I initiation factor, designated TFIC. The data indicate that initiation by RNA polymerase I is a multi-step process. The first step involves the formation of stable, preinitiation complexes, as demonstrated by a number of groups. Initiation, per se, requires an additional protein, TFIC. Glucocorticoids and perhaps other mitogenic agents regulate transcription of rDNA by influencing the amount or activity of TFIC.
D000818:Animals; D002478:Cells, Cultured; D004275:DNA, Ribosomal / Q000378:metabolism*; D003907:Dexamethasone / Q000494:pharmacology*; D008970:Molecular Weight; D010441:Peptide Chain Elongation, Translational / Q000187:drug effects*; D010442:Peptide Chain Initiation, Translational / Q000187:drug effects*; D012318:RNA Polymerase I / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects
D004275:DNA, Ribosomal; D003907:Dexamethasone; D012318:RNA Polymerase I