The structure of aldolase isozyme genes and the regulation of their tissue-specific expression

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By examining the tissues and cells which express or do not express aldolase B gene, the relationship between the gene expression and chromatin structure and DNA methylation of aldolase B gene was studied. Following results were obtained. (1) The examination of the chromatin structure of aldolase B locus by DNase I hypersensitivity revealed that the specific structure which is sensitive to DNase I at about 0.3 Kb upstream from the transcription-initiation site is necessary for transcription of the gene. (2) Out of 15 Hpa <II> and Hha <I> sites in and around the gene, those sites which located at 3'-half and at downstream of the gene were heavily methylated, regardless of the gene expression. A Hha <I> site in the 5'-flanking region, and several Hpa <II> sites in the first intron were hypomethylated in liver and differentiated hepatoma, while they were heavily methylated in brain and undifferentiated hepatoma. These facts suggest that the hypomethylation of cytosine residue at specific sites in the 5'-flanking and the 5'-half regions of the gene are related to the expression of this gene. Our recent results suggest that, besides loosened chromatin structure and hypomethylation, some trans-acting factor(s) which interact with the element in this region are necessary for the transcription of this gene.