Propagation of globin DNAase i-hypersensitive sites in absence of factors required for induction: A possible mechanism for determination

Abstract

We tested whether DNAase I-hypersensitive sites, once induced, can be propagated to daughter cells in the absence of the original inducer. Chicken embryo fibroblasts infected with a temperature-sensitive Rous sarcoma virus at 41 °C and then shifted to 36°C become transformed and begin to transcribe globin RNA. DNAase I-hypersensitive sites appear in the α- and β-globin chromatin domains. Neither transcription nor hypersensitive sites are detected in cells infected and maintained at 41°C. Activation of the globin hypersensitive sites occurs within 30 min of a temperature shift to 36°C and does not require new protein synthesis. To test for the self-propagation of these hypersensitive structures, we inactivated the v-src gene product by a shift back up to 41°C, and allowed the cells to divide 20 times at 41°C. Although transcription of the globin genes was minimal after this treatment, the DNAase I-hypersensitive sites remained. The same sites can be induced by NaCI shock of cells. After the cells are returned to normal medium and allowed to grow for 20 doublings, the hypersensitive sites remain. This suggests that once formed, DNAase I-hypersensitive sites have the capacity to template their own structure independent of the initial “inductive” event. The single-stranded character of these DNAase I-hypersensitive sites could explain these results.