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J. Biol. Chem., Vol. 265, Issue 15, 8775-8781, 05, 1990
NC Wong, BJ Deschamps, ZA Yeomans and PD Cannon
The rat hepatic S14 gene is regulated by L-triiodothyronine (T3) and codes
for a cytosolic protein (pI 4.9 and Mr 17,010) that is believed to be
involved in lipogenesis. Recent studies have identified at least five DNase
I hypersensitive sites (HS 1-5) in hepatic chromatin flanking the 5' region
of the gene. The HS-1 site is situated immediately adjacent to the
transcription initiation site. We have isolated a DNA fragment (USS-1)
which contains a portion of the HS-1 site to examine the binding of nuclear
proteins to S14 DNA. DNase I footprinting studies demonstrated that
material extracted from hepatic nuclei with 0.42 M NaCl contained
proteinase K-sensitive factors (presumed to be proteins), which bind to
USS-1 DNA between positions - 63 and -48 (PS-1) relative to the
transcription initiation site. Examination of the binding activity with a
synthetic oligonucleotide identical to the protected sequence indicated the
formation of at least three protein-DNA complexes. The DNA binding activity
of the PS-1 binding protein or proteins correlated with the T3 regulated
expression of mRNA-S14. Although the nucleotide sequence of PS-1 closely
resembles the binding site for the CCAAT transcription factor (CTF/NF-1),
competition studies attempting to displace protein binding from the PS- 1
sequence with DNA fragments containing the CTF/NF-1 binding motif were
unsuccessful. In vitro transcriptional assay studies suggested that the DNA
fragment (-441 to -2) containing the PS-1 site promotes the transcription
of the S14 gene in an orientation fashion. The in vitro transcriptional
activity of the S14 DNA containing the PS-1 sequence was significantly
higher in hepatonuclear extracts from hyperthyroid compared with euthyroid
or hypothyroid animals. In summary, our findings indicate that the DNA
binding activity of proteins which bind to PS-1 site is influenced by the
thyroid status of the animal.
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