Brown S A, Weirich C S, Newton E M, Kingston R E
Department of Genetics, Harvard Medical School, and Department of Molecular Biology, Massachusetts General Hospital, Boston, MA 02114, USA.
EMBO J. 1998 Jun 1;17(11):3146-54. doi: 10.1093/emboj/17.11.3146.
Transcriptional activators can stimulate multiple steps in the transcription process. We have used GAL4 fusion proteins to characterize the ability of different transcriptional activation domains to stimulate transcriptional elongation on the hsp70 gene in vitro. Stimulation of elongation apparently occurs via a mechanistic pathway different from that of stimulation of initiation: the herpes simplex virus VP16, heat shock factor 1 (HSF1) and amphipathic helix (AH) activation domains all stimulate initiation, but only VP16 and HSF1 stimulate elongation; and mutations in hydrophobic residues of the HSF1 activation domains impair stimulation of elongation but not of initiation, while mutations in adjacent acidic residues impair stimulation of initiation more than of elongation. Experiments in which activators were exchanged between initiation and elongation demonstrate that the elongation function of HSF1 will stimulate RNA polymerase that has initiated and is transcriptionally engaged. Transcriptional activators thus appear to have at least two distinct functions that reside in the same domain, and that act at different times to stimulate initiation and elongation.
转录激活因子可以刺激转录过程中的多个步骤。我们利用GAL4融合蛋白在体外表征了不同转录激活结构域刺激hsp70基因转录延伸的能力。延伸的刺激显然是通过一条与起始刺激不同的机制途径发生的：单纯疱疹病毒VP16、热休克因子1（HSF1）和两亲性螺旋（AH）激活结构域都能刺激起始，但只有VP16和HSF1能刺激延伸；HSF1激活结构域中疏水残基的突变会损害延伸刺激，但不会损害起始刺激，而相邻酸性残基的突变对起始刺激的损害比对延伸刺激的损害更大。在起始和延伸之间交换激活因子的实验表明，HSF1的延伸功能将刺激已起始并正在进行转录的RNA聚合酶。因此，转录激活因子似乎至少有两种不同的功能，它们存在于同一结构域中，并在不同时间起作用以刺激起始和延伸。
