IDENTIFICATION OF TRANSCRIPTIONALLY INDUCED Z-DNA SEGMENTS IN THE HUMAN C-MYC GENE

Using monoclonal antibodies against Z-DNA three AluI restriction fragm ents of the human c-myc gene were previously found to form Z-DNA in ag arose-embedded, metabolically active permeabilized nuclei. The formati on of Z-DNA in these fragments was dependent on negative supercoiling generated by transcription of the gene. Here we show which sequence el ements of these three AluI restriction fragments adopt the Z conformat ion upon negative supercoiling. The three fragments (Z1, Z2 and Z3) we re inserted in a suitable plasmid vector. Z-DNA forming elements were detected by comparing DEPC reactivity in relaxed circular and supercoi led plasmid DNA. Z1 and Z3 each contained one major Z-DNA forming regi on 20-25 nucleotides long, whereas Z2 contained two discrete regions 9 0 nucleotides apart one about 35 nucleotides the other about 20 nucleo tides long.