PUB - Publikationen an der Universität Bielefeld

BACKGROUND:
Despite the profound current knowledge of the architecture and dynamics of nucleosomes, little is known about the structures generated by the interaction of histones with single-stranded DNA (ssDNA), which is widely present during replication and transcription.
METHODS:
Non-denaturing gel electrophoresis, transmission electron microscopy, atomic force microscopy, magnetic tweezers.
RESULTS:
Histones have a high affinity for ssDNA in 0.15M NaCl ionic strength, with an apparent binding constant similar to that calculated for their association with double-stranded DNA (dsDNA). The length of DNA (number of nucleotides in ssDNA or base pairs in dsDNA) associated with a fixed core histone mass is the same for both ssDNA and dsDNA. Although histone-ssDNA complexes show a high tendency to aggregate, nucleosome-like structures are formed at physiological salt concentrations. Core histones are able to protect ssDNA from digestion by micrococcal nuclease, and a shortening of ssDNA occurs upon its interaction with histones. The purified (+) strand of a cloned DNA fragment of nucleosomal origin has a higher affinity for histones than the purified complementary (-) strand.
CONCLUSIONS:
At physiological ionic strength histones have high affinity for ssDNA, possibly associating with it into nucleosome-like structures.
GENERAL SIGNIFICANCE:
In the cell nucleus histones may spontaneously interact with ssDNA to facilitate their participation in the replication and transcription of chromatin.
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