THE TRIPARTITE DNA ELEMENT RESPONSIBLE FOR DIET-INDUCED RAT FATTY-ACID SYNTHASE (FAS) REGULATION

We investigated which region of the 5'-flanking sequence of the rat fatty acid synthase (FAS)-encoding gene could be responsible for its nutritionally regulated expression. Diet-induced differences in chromatin structure were determined by DNase I treatment of intact nuclei from hepatic tissue. A low-fat diet results in a different pattern of DNase I-hypersensitive sites (HS) in the chromatin of the FAS promoter (pFAS) from that seen when the nuclear extract was prepared from the livers of normally fed rats. The protein-binding properties of the region defined by DNase I hypersensitivity were tested by gel retardation. A putative cis-acting element with a tripartite structure, 5'-GCCT, 6-bp spacer and a 3'-palindrome, could be localized between bp -518 to -495 in pFAS. Competition experiments with oligodeoxyribonucleotides (oligos) representing subfragments of this cis-element showed that the requirement for structure is stricter than that for sequence. This element could be one of the termini of the insulin-induced signal cascade.