A DNA region containing several repetitive motifs has been detected about 1.9 kbp upstream of the transcription unit of the rat stress-inducible hsp70.1 gene. The most interesting element of this area is a microsatellite sequence (GA)eCAG(TC)24 that consists of an inverted repeat partially overlapping with the long homopurine/homopyrimidine tract (Pu/Py). DNA molecule within the described sequence can theoretically adopt alternate, non-B structures (H-DNA or cruciform) containing single-stranded regions. This microsatellite region is flanked by AT-rich sequences containing several poly(A) tracts. The longest of them with a possible potential to destabilize a double-stranded DNA helix is localized around 160 bp downstream the (GA)6CAG(TC)24. The DNA fragment containing sequences described above was subcloned into the pUCl9 vector and the resulting plasmid was subjected to the standard SI susceptibility assay. Preliminary mapping of the SI cleavage site indicates for the formation of the non-B-DNA structure within the Pu/Py tract. This is to our knowledge a first report on the existence of a complex microsatellite region upstream the 5'-end of the hsp70 gene in mammals.
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