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The dependence of the linking number of a circular minichromosome upon the shape and the orientation of its nucleosomes
Author(s) -
Grigoryev Sergei A.,
Ioffe Lev B.
Publication year - 1981
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(81)80661-8
Subject(s) - minichromosome , citation , physics , library science , biology , computer science , genetics , dna , chromatin
It is now well established that a DNA molecule makes 1 S-2.0 left superhelical turns around an octamer of histones in the unit structure of eucaryotic chromatin, the nucleosome [l]. The formation of a chain of nucleosomes, a minichromosome, with histones H2A, H2B, H3 and H4 and circular, covalently closed DNA (ccDNA) in the presence of nickingclosing enzyme is coupled with the alteration of the linking number, i.e., the number of topological revolutions made by one strand about the other in the ccDNA molecule. The linking number is altered by -1 per one nucleosome [2,3] whereas the existing theory [4-61 predicts this change to be equal to the sum of turns made by DNA in each nucleosome, that is -1.7 per one nucleosome. We have found out that the predicted change of the linking number is inherent in minichromosomes with parallel orientation of nucleosomal axes which is not consistent with real minichromosome structure. The linking number values for minichromosomes with constant and random angles between their nucleosomes are calculated here. The results obtained permit one to eliminate the contradictions between linking number theory and experiments.