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Elastic torsional strain in DNA within a fraction of SV40 minichromosomes: relation to transcriptionally active chromatin.
Author(s) -
Luchnik A.N.,
Bakayev V.V.,
Zbarsky I.B.,
Georgiev G.P.
Publication year - 1982
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1002/j.1460-2075.1982.tb01322.x
Subject(s) - biology , chromatin , dna , strain (injury) , genetics , minichromosome , microbiology and biotechnology , anatomy
After treatment of SV40 minichromosomes with DNA topoisomerase I, the superhelicity in the bulk of the DNA extracted from minichromosomes is known to remain unchanged. However, we found that the DNA extracted from a small fraction of SV40 minichromosomes (2‐5%), was almost completely relaxed, and covalently closed as shown by agarose gel electrophoresis. Thus, the DNA in these 2‐5% of SV40 minichromosomes was probably torsionally strained (TS). The proportion of such TS minichromosomes is close to the estimated proportion of transcriptionally active minichromosomes. The distribution of the TS minichromosomes in sucrose gradient coincided with the distribution of transcriptionally active complexes. Both sedimented faster than the majority of minichromosomes. Furthermore, after treatment with topoisomerase I the relaxed minichromosomes could be quantitatively separated from the bulk of material by recentrifugation in a sucrose gradient. A major part of the endogenous RNA polymerase activity was recovered in the relaxed fraction. These data suggest that TS‐minichromosomes correspond to transcriptionally active chromatin. After relaxation with topoisomerase I the TS minichromosomes lacked histones.