Molecular and Cellular Biology, December 1999, p. 7951-7960, Vol. 19, No. 12
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Department of Biology,
Received 14 May 1999/Returned for modification 29 June
1999/Accepted 2 September 1999
We previously identified a novel TATA-binding protein
(TBP)-interacting protein (TIP120) from the rat liver. Here, in an RNA polymerase II (RNAP II)-reconstituted transcription system, we demonstrate that recombinant TIP120 activates the basal level of
transcription from various kinds of promoters regardless of the
template DNA topology and the presence of TFIIE/TFIIH and TBP-associated factors. Deletion analysis demonstrated that a 412-residue N-terminal domain, which includes an acidic region and the
TBP-binding domain, is required for TIP120 function. Kinetic studies
suggest that TIP120 functions during preinitiation complex (PIC)
formation at the step of RNAP II/TFIIF recruitment to the promoter but
not after the completion of PIC formation. Electrophoretic mobility
shift assays showed that TIP120 enhanced PIC formation, and TIP120 also
stimulated the nonspecific transcription and DNA-binding activity of
RNAP II. These lines of evidence suggest that TIP120 is able to
activate basal transcription by overcoming a kinetic impediment to RNAP
II/TFIIF integration into the TBP (TFIID)-TFIIB-DNA-complex. Interestingly, TIP120 also stimulates RNAP I- and III-driven
transcription and binds to RPB5, one of the common subunits of the
eukaryotic RNA polymerases, in vitro. Furthermore, in mouse cells,
ectopically expressed TIP120 enhances transcription from all three
classes (I, II, and III) of promoters. We propose that TIP120 globally regulates transcription through interaction with basal transcription mechanisms common to all three transcription systems.
*
Corresponding author. Mailing address: Department of
Biology, Faculty of Science, Chiba University, 1-33 Yayoi-cho,
Inage-ku, Chiba 263-8522, Japan. Phone: (81) 43-290-2823. Fax: (81)
43-290-2824. E-mail: btamura{at}nature.s.chiba-u.ac.jp.
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