| Co-Investigator(Kenkyū-buntansha) |
TAMATE Hidetoshi The Department of Biochemistry, Assistant, 医学部, 助手 (90163675)
TSUTSUMI Reiko The Department of Nuclear Medicine, Assistant, 医学部付属病院, 助手 (20005664)
TSUTSUMI Ken-ichi Yamagata University School of Medicine, The Department of Biochemistry, Assistan, 医学部, 助教授 (40113964)
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| Research Abstract |
The aim of this work was to identify (1) the cis-elements in the promoter of aldolase B (AldB) gene for the tissue-specific transcription of this gene in the liver, and (2) the trans-factors which bind to these cis-elements. For the last two years, we have been able to show that there are three such cis-elements, A-site (-98/-123), B-site (-116/-138), and C-site (-139/-157), within the promoter of AldB gene, and at least three trans-factors, AlF-A, AlF-B, and AlF-C, which bind to A-, B-, and C-sites, respectively.
AlF-A seems to be the protein with the molecular weight of about 70 Kd. Its binding to A-site is competitively inhibited by the cis-element in the promoter of albumin gene for HNF-1/LFB-1, thus suggesting that this factor is the one similar, if not identical, to HNP-1/LFB-1.
AlF-B is one of the CAAT-binding proteins, since the B-site contains CAAT motif sequence. The heat-stability, tissue-specificity, and molecular weight of AlF-B do not resemble those of other CAAT-binding proteins so far reported, such as CBP, CTF/NF-1, NF-Y, and C/EBP. Therefore, it is probable that AlF-B is a novel CAAT-binding protein.
The binding of this factor to the B-site element is inhibited completely with the cytidine methylation in vitro at the position two nucleotide upstream of the CAAT motif (-GC*GCCAAT-). Our previous study showed that hypomethylation at this position is essential for the expression of AldB gene in vivo. This finding supports that AlF-B binding to the B-site element id important for the transcription of this gene in vivo.
In conclusion, we have been able to show that the tissue-specific transcription of AldB gene in the liver is controlled primarily by trans-factors, AlF-A, AlF-G, and AlF-C. Besides these trans-factors, the methylation of one of the cis-elements, the B-site element, has another important role in the tissue-specific transcription of this gene. Thus, the tissue-specific transcription of AldB gene is doubly regulated.
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