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Molecular and Cellular Biology, July 1999, p. 5218-5234, Vol. 19, No. 7
Department of Biochemistry and Molecular
Biology, Program of Molecular Biology, Microbiology, and
Biochemistry, Southern Illinois University School of Medicine,
Carbondale, Illinois 62901-4413
Received 24 July 1998/Returned for modification 1 September
1998/Accepted 29 March 1999
The interaction of yeast TFIIIB with the region upstream of the
SUP4 tRNATyr gene was extensively probed by use
of photoreactive phosphodiesters, deoxyuridines, and deoxycytidines
that are site specifically incorporated into DNA. The TATA binding
protein (TBP) was found to be in close proximity to the minor groove of
a TATA-like DNA sequence that starts 30 nucleotides upstream of the
start site of transcription. TBP was cross-linked to the phosphate
backbone of DNA from bp
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Spatial Organization of the Core Region of Yeast
TFIIIB-DNA Complexes
30 to
20 in the nontranscribed strand and
from bp
28 to
24 in the transcribed strand (+1 denotes the start
site of transcription). Most of the major groove of DNA in this region
was shown not to be in close proximity to TBP, thus resembling the
binding of TBP to the TATA box, with one notable exception. TBP was
shown to interact with the major groove of DNA primarily at bp
23 and to a lesser degree at bp
25 in the transcribed strand. The stable interaction of TBP with the major groove at bp
23 was shown to require the B" subunit of TFIIIB. The S4 helix and flanking region of
TBP were shown to be proximal to the major groove of DNA by peptide
mapping of the region of TBP cross-linked at bp
23. Thus, TBP in the
TFIIIB-SUP4 gene promoter region is bound in the same direction as TBP bound to the TATA box with respect to the
transcription start site. The B" and TFIIB-related factor (BRF)
subunits of TFIIIB are positioned on opposite sides of the TBP-DNA core
of the TFIIIB complex, as indicated by correlation of cross-linking data to the crystal structure of the TBP-TATA box complex. Evidence is
given for BRF binding near the C-terminal stirrup of TBP, similar to
that of TFIIB near the TBP-TATA box complex. The protein clamp formed
around the TBP-DNA complex by BRF and B" would help explain the long
half-life of the TFIIIB-DNA complex and its resistance to polyanions
and high salt. The path of DNA traversing the surface of TBP at the 3'
end of the TATA-like element in the SUP4 tRNA gene is not
the same as that of TBP bound to a TATA box element, as shown by the
cross-linking of TBP at bp
23.
*
Corresponding author. Mailing address: Department of
Biochemistry and Molecular Biology, Southern Illinois University School of Medicine, 1245 Lincoln Dr. #229C, Carbondale, IL 62901-4413. Phone:
(618) 453-6437. Fax: (618) 453-6440. E-mail:
bbartholomew{at}som.siu.edu.
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