CHROMATIN STRUCTURE WITHIN SITES OF DNA REPLICATION
S. A. Golyshev, V. Yu. Polyakov
A. N. Belozersky Institute of Physico-Chemical Biology, Moscow State University;
e-mail: sergei.golyshev@mail.genebee.msu.ru
Conformational changes in chromatin structure are nowadays the object of intensive research due to its importance
for proper regulation of intranuclear processes. The fine structure of chromatin within the DNA replication
sites was studied in in situ fixed cells and cells permebilized by low ionic strength solutions in the presence
of divalent cations. The latter method provides visualization of higher level chromatin structures such as globular
chromomeres and chromonema fibres. Nascent DNA was detected immunochemically using anti-BrdU
antibodies on the surface of ultrathin sections prepared from Epon-embedded material. It was shown that newly
replicated DNA preferentially localized within the zones filled with globular and fibrillar elements with characteristic
diameter of 30 nm, and not in chromonema fibres, while after replication had been completed DNA
became embedded into as thick as 60-80 nm chromonema elements. The results obtained are discussed in
the context of conception of hierarchical folding of chromatin fibers.
Key words: DNA replication, replication site, chromatin, chromonema, chromomere, nucleomere,
electron microscopy
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