Hormonal regulation of transcription of rDNA: glucocorticoid effects upon initiation and elongation in vitro

Abstract

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.