Visible light induced DNA-protein crosslinking in DNA-histone complex and sarcoma-180 chromatin in the presence of methylene blue.
Formation of DNA-protein cross-links by the action of visible light in the presence of methylene blue was studied in calf thymus DNA-calf thymus histone complex and sarcoma-180 chromatin. The extent of cross-link formation decreases with a decrease in the histone to DNA ratio in the DNA-histone complex. In chromatin, it is at a maximum (93%) at a dye to DNA nucleotide ratio (D/P ratio) of 0.04 and is appreciable even at a very low dye concentration (75% at a D/P ratio of 0.0033). Sepharose 4B-CL column chromatography indicates that methylene blue acts as a mediator in the cross-linking process, but not as a linker in the DNA-protein cross-link. Dodecylsulphate-polyacrylamide gel electrophoresis patterns reveal that both histone and non-histone proteins are involved in cross-linking, but to a varied extent. Competition experiments with ethidium bromide demonstrated the necessity of intercalative binding of methylene blue in the formation of DNA--protein cross-links. Viscometric studies in 2 M NaCl indicate that the compact structure of chromatin is stabilized by cross-linking.
Lalwani
R
R
Department of Biophysics, Chittaranjan National Cancer Institute Calcutta, India.
Maiti
S
S
Mukherji
S
S
D000818:Animals; D002843:Chromatin / Q000737:chemistry / Q000528:radiation effects; D003432:Cross-Linking Reagents; D004247:DNA / Q000737:chemistry / Q000528:radiation effects*; D006657:Histones / Q000737:chemistry / Q000528:radiation effects; D008027:Light; D008297:Male; D008751:Methylene Blue; D051379:Mice; D010777:Photochemistry; D011506:Proteins / Q000737:chemistry / Q000528:radiation effects*; D012510:Sarcoma 180 / Q000378:metabolism
D002843:Chromatin; D003432:Cross-Linking Reagents; D006657:Histones; D011506:Proteins; D004247:DNA; D008751:Methylene Blue