ИСТИНА

Nucleosome is a structural unit of chromatin consisting of ~145 bp DNA wrapped around a histone octamer. Of interest is the interaction of disordered histone tails with nucleosomal DNA; in the case of histone H3, this issue is most relevant since histone H3 has a long unstructured N-terminal tail and its interaction with DNA occurs at a functionally significant region of the nucleosomal dyad. The interaction of the positively charged histone tail and DNA is realized through electrostatic interactions, the effectiveness of which depends on the ionic strength of the solution and, accordingly, the concentration of ions in the solution. In our work, NaCl concentrations of 20 and 100 mM were chosen to study these interactions. We prepared samples with nucleosome core particles. DNA sequence Widom 601 (145 bp) was used as nucleosomal DNA; the histone octamer included canonical human histones H2A, H2B, H4 and 15N-labeled H3.1. To assess the mobility of the histone H3 tail, measurements of the R1 parameter were carried out first at a NaCl concentration of 20 mM, then at 100 mM. A Bruker Avance III 700 MHz NMR spectrometer equipped with a cryoprobe was used. According to NMR data, with increasing NaCl concentration, an increase in the value of the R1 parameter was observed for the amino acid residues selected for analysis: S11, T12, G13, K15, S29, T33, V36. The observed trend may be due to weakening of electrostatic interactions between the histone H3 tail and nucleosomal DNA, which leads to increased mobility of histone tails.