Circular dichroism studies of ethidium bromide binding to the isolated nucleolus

Open Access
Publisher Website
Google Scholar
Abstract
Circular dichroism in the 300–360 nm region and fluorescence induced by intercalating binding of ethidium bromide to both DNA and RNA components were studied in isolated HeLa nucleoli. Both DNA and RNA components contribute to the induced dichroic ellipticity. Digestion of nucleoli by RNase or DNase shows that most of the induced ellipticity comes from the DNA component. In nucleoli with an RNA/DNA = 0.8/1.0 the RNA component gives only 20% of the total ellipticity when measured at an ethidium bromide/DNA = 0.25.Spectrofluorometric titration shows that ethidium bromide intercalates mostly into DNA in nucleoli. Both circular dichroism and fluorescence studies indicate that both DNA and RNA components in isolated nucleoli are less accessible to intercalating binding by ethidium bromide when compared to purified nucleolar DNA, DNA in chromatin or purified ribosomal RNA. Circular dichroic measurements of intercalating binding of ethidium bromide to nucleoli may be used to study changes in nucleoli under different physiological or pathological conditions.