Biophysical characterization of the association of histones with single-stranded DNA

Publication date: Available online 27 July 2017
Source:Biochimica et Biophysica Acta (BBA) - General Subjects
Author(s): Ying Wang, Luis van Merwyk, Katja Tönsing, Volker Walhorn, Dario Anselmetti, Xavier Fernàndez-Busquets
BackgroundDespite 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.MethodsNon-denaturing gel electrophoresis, transmission electron microscopy, atomic force microscopy, magnetic tweezers.ResultsHistones have a high affinity for ssDNA at physiological salt concentrations, 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. Whereas histone-ssDNA complexes show a high tendency to aggregate in 0.2 M NaCl, at lower ionic strength nucleosome-like structures are formed. 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.ConclusionsAt physiological ionic strength histones have high affinity for ssDNA, possibly associating with it into nucleosome-like structures.General SignificanceIn the cell nucleus histones may spontaneously interact with ssDNA to facilitate their participation in the replication and transcription of chromatin.



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