Transcriptional activation domains stimulate initiation and elongation at different times and via different residues.
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.
Brown
S A
SA
Department of Genetics, Harvard Medical School, and Department of Molecular Biology, Massachusetts General Hospital, Boston, MA 02114, USA.
Weirich
C S
CS
Newton
E M
EM
Kingston
R E
RE
D000595:Amino Acid Sequence; D004268:DNA-Binding Proteins / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D018840:HSP70 Heat-Shock Proteins / Q000096:biosynthesis / Q000235:genetics; D006367:HeLa Cells; D000076249:Heat Shock Transcription Factors; D006360:Heat-Shock Proteins / Q000502:physiology; D006801:Humans; D008969:Molecular Sequence Data; D009707:Nucleosomes / Q000235:genetics / Q000502:physiology; D010441:Peptide Chain Elongation, Translational / Q000187:drug effects / Q000235:genetics*; D010442:Peptide Chain Initiation, Translational / Q000187:drug effects / Q000235:genetics*; D017434:Protein Structure, Tertiary; D015534:Trans-Activators / Q000502:physiology; D014157:Transcription Factors; D015533:Transcriptional Activation / Q000502:physiology*
D004268:DNA-Binding Proteins; C000619706:HSF1 protein, human; D018840:HSP70 Heat-Shock Proteins; D000076249:Heat Shock Transcription Factors; D006360:Heat-Shock Proteins; D009707:Nucleosomes; D015534:Trans-Activators; D014157:Transcription Factors