Mixed Conformations of Deoxyribonucleic Acid in Chromatin: a Preliminary Report

Overview

Journal Proc Natl Acad Sci U S A

Specialty Science

Date 1972 Nov 1

PMID 4343960

Citations 12

Authors

S Hanlon

R S Johnson

B Wolf

A Chan

Affiliations

Soon will be listed here.

Abstract

We have established empirical limits for the circular dichroism spectra appropriate for aqueous solutions of the B, C, and A forms of calf-thymus DNA and have analyzed DNA conformations in biological structures. The circular dichroism spectrum above 250 nm of purified calf-thymus chromatin can be satisfactorily accounted for as a linear combination of contributions of the B and C reference spectra without invoking higher-order structures such as supercoils. The amount of A contribution, if any, is below the limit of detection (</=4%). The fraction of bases in the B conformation depends on the method of isolation of nucleohistone, and ranges from 30-50%. The B content of a given preparation is increased by addition of a chelating agent and decreased by addition of divalent ions. More radical increases ensue upon protein removal. Nuclease treatment results in a dramatic decrease in B content. The fraction of bases melting out in the lower transitions of the complex melting profile of a given chromatin preparation corresponds to its B content. We propose a model for chromatin structure in which part of the DNA duplex is exposed or accessible to the solvent and is in the B conformation. The remainder of the base pairs and ribophosphate backbone are protected from interaction with the solvent by efficient histone coverage and are in the C conformation. Divalent ions modulate the distribution of bases between these two conformations.

Citing Articles

Dye-nucleoprotein interactions in Giemsa banding.

Meisner L, Chuprevich T, Inhorn S, Johnson C J Cell Biol. 1974; 61(1):248-53.

PMID: 4132066 PMC: 2109271. DOI: 10.1083/jcb.61.1.248.

A study of the interaction between ethidium bromide and rye chromatin: comparison with calf thymus chromatin.

Larue H, Pallotta D Nucleic Acids Res. 1976; 3(9):2193-206.

PMID: 987580 PMC: 343076. DOI: 10.1093/nar/3.9.2193.

Conformational states of chromatin nu bodies induced by urea.

Olins D, Bryan P, Harrington R, Hill W, Olins A Nucleic Acids Res. 1977; 4(6):1911-31.

PMID: 896477 PMC: 342531. DOI: 10.1093/nar/4.6.1911.

Salt-induced structural changes in nucleosomes.

Sahasrabuddhe C, Saunders G Nucleic Acids Res. 1977; 4(4):853-66.

PMID: 866195 PMC: 342489. DOI: 10.1093/nar/4.4.853.

Secondary structure of nucleic acids in the folded chromosome from E. coli.

Baase W, Johnson Jr W Nucleic Acids Res. 1976; 3(11):3123-31.

PMID: 794834 PMC: 343156. DOI: 10.1093/nar/3.11.3123.

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