Mechanisms of chromosome banding

Abstract

The binding of methylene blue to DNA and chromatin treated in various ways was examined by equilibrium dialysis. The maximum r value (moles of bound dye/mole of nucleotide) was 1.0 for DNA, 0.6 for unfixed chromatin, and 0.83 for chromatin fixed in methanol-acetic acid. When fixed chromatin was treated with saline-citrate at 60 degrees C for 3 hours, as used for G-banding chromosomes, the r value decreased from 0.83 to 0.55. When unfixed chromatin was treated as for R-banding the r values also dropped. Equilibrium dialysis indicated there was no disproportionate increase of dye binding as the concentration of DNA increased. -- These results, and others, suggest that some of the Giemsa negative regions of G- and R-banded chromosomes are due to the denaturation of non-histone proteins so that they more effectively cover the DNA and prevent side binding of the thiazin dyes.

The Effect of Magnesium Ions on Chromosome Structure: Insights from G-Banding

“…Moreover, the bands in the chromosome treated with EDTA were still visible, although the produced G-bands were unclear with low intensity. As a consequence of chromosome decondensation, the complex dye was not adequately formed because the dye could not intercalate into the chromosome structure which prevents the binding of the dye, where this condition led to poorly stained bands 24 . These results implied that different degrees of chromatin condensation affected the accessibility of DNA to the binding of the dye 25 .…”

Histones and G Banding of Chromosomes

“…Ac tein to the fixed chro] these phosphate groups concentration prevents tl from binding. This is a ni related to the charge den protein and does not o that histones are involve Equilibrium dialysis stuo ylene blue and fixed ch by conditions used in G suggest that some of the gions are in part the res binding of nonhistone pr thus preventing the bin dyes (18).…”

“…At saturation, These preparations are never exposed to r ratio for naked conditions that would extract any hisd chromatin the tones, and yet the chromosome of mitotvhile with fixed ic cells stain intensely with these dyes. 0.8 (18), an in-The same is true of cells in tissue culture. nany free phos-If they are fixed on a slide in ethanol, foror forming com-malin, or glutaraldehyde, so that the his-Iding basic pro-tones are not removed, the metaphase mosomes binds chromosomes still stain intensely.…”

“…With unfixe ratio is 0.5 (17,18), M chromatin the ratio is dication that there are r phate groups available ft plexes with the dye. Ac tein to the fixed chro] these phosphate groups concentration prevents tl from binding.…”

“…(ii) onspecific effect Dye binding studies show that whole isity of the basic chromatin, with its full complement of of itself indicate histones, binds 0.5 mole of thiazine dye d in G banding. per mole of DNA phosphate, and this is dies with methmore than adequate to stain the chroma-[romatin treated tin (17,18). and R banding…”