Fold-back tetraplex DNA species in DNase I-resistant DNA isolated from HeLa cells

A DNase I-resistant DNA species has been isolated and purified from HeLa ce lls by gel electrophoresis. Our studies indicate that the DNase I-resistant DNA species was about 40-60 bp fragment sizes responding to double-strand DNA marker and has higher guanine content. The image of AFM showed that thi s species has been assumed to be tetraplex structure according to its appar ent width and height. Its CD, UV spectrum also exhibited characteristics si milar to some tetraplex structure, which was different from the standard du plex DNA. P-32-labeled probes (TTAGGG)(4) and 5'-TGGGGAGGGTGGGGAGGGTGGGGAAG G-3' could be hybridized to purified DNase I-resistant species. All results suggest that the DNase I-resistant DNA species have at least two component s, which adopt an intrastrand fold-back DNA tetraplex. Their sequences were similar to human telomere and human c-myc locus (NHE), respectively.