Analysis of chromatin structure at the AZU1-PRTN3-ELA2-ADN (APEA) locus in untreated U-937 cells. Nuclei were prepared and treated with increasing concentrations of DNase I (0 to 5 μg/mL, increasing from left to right in each case). The location of molecular weight DNA markers are shown on the left, in kilobases. DHS are indicated by solid arrowheads, with DHS-1 lying toward the AZU1 portion of the locus and DHS-15 at the ADN end of the locus. (A) DHS-1 to -4. DNase I–treated DNA was digested to completion with EcoRI and hybridized with a PCR amplified, ³²P-labeled AZU1 exon 4/5 cDNA probe. (B) DHS-5 to -10. DNase I–treated DNA was digested to completion with Mlu I and hybridized with a PCR-amplified ELA2 exon I/II probe. (C) DHS-16 and -17. DNase I–treated DNA was digested to completion with Eco RI and hybridized with a ³²P-labeled ADN cDNA probe. (D) DHS-11 and -12. DNase I–treated DNA was digested to completion with Bam HI and hybridized with a ³²P-labeled ELA2 exon IV/V probe.