Effects of a DNA Intercalator, Ethidium Bromide on Chromatin Structure of Chicken Erythrocyte

Abstract

DNase I hypersensitive sites (DHS) are the most loosely packed regions in chromatin, which are ultrasensitive, typically 100 times more than bulk chromatin, to DNase I as well as other DNA cleaving agents including methidiumpropy EDTA, a DNA intercalator (Elgin, 1988; Gruss and Garrard, 1988). DHS have been mapped to many functionally crucial regions, including promoter, enhancer, silencer and terminator of transcription, DNA replication origins, recombination elements as well as the centromere and telomere. Relevant to the transcription of genes, the occurrence of DHS can be constitutive or inducible, and developmentally or tissue-specifically regulated. DHS have been correllated with the chromatin region of nucleosome-free, or of atypical DNA structure, or associated with trans-acting protein or proteins, or both. Conformational polymorphism of the DNA component of genome, notably bending, unpairing, cruciform and Z-form, is both sequence and environment-dependant (Rich et al., 1984; McLean and Wells, 1988; Jaworski et al., 1987). DNA supercoiling (Tsao et al., 1989) and DNA binding proteins are two important environmental factors. The former may also play a role in formation and maintenance of DHS (Villeponteau, et al., 1984). DNA-protein interaction, especially the sequence-specific interaction (Pabo and Sauer, 1986; Dynan and Tjian, 1985), may also participate in formation of DHS in vivo (Emerson and Felsenfeld, 1984). DNA intercalators alter DNA conformation by inserting their planer aromatic rings between the base pairs of the neighbouring nucleotides, without impairing the structural integrity of DNA (Neidle and Abraham, 1984).