A nucleosome is the structural part of a chromosome formed by co-packaging a DNA strand with histone proteins H2A, H2B, H3 and H4. A sequence of nucleosomes connected by the histone protein H1 forms a nucleofilament , or otherwise a nucleosome strand.
Around the nucleosomal nucleus represented by the histone octamer, DNA makes 1.67 turns (147 bp). The portion of DNA between the nucleosomes is called linker DNA and is 10-100 bp.
Nucleosome assembly occurs on DNA. During DNA replication, maternal histones are randomly distributed across daughter chains. Histone chaperones temporarily shield the charge of histones , ensuring the correct assembly of the nucleosome. Chaperone CAF1 is bound to PCNA , sits in a replication fork, linking the "old" H3H4 dimers, and begins the replication of nucleosomes after planting this dimer.
Despite the fact that the nucleosome binds DNA regardless of the sequence, different DNA sequences can differ 1000 times in potential to bind the nucleosome. If successive sequences follow that bend the DNA in one direction (for example, TATA), nucleosome binding will be unstable.
The genome contains:
- nucleosome-free sites ( open chromatin : binding sites for transcription factors, regulatory proteins);
- areas where the position of the nucleosome is strictly fixed (for example, the start of transcription of many genes);
- areas in which the nucleosome folding is subject to regulation by proteins of ATP-dependent chromatin remodeling .
See also
- Nucleosome positioning
Literature
- Zhimulev I.F. General and molecular genetics. - 1. - Novosibirsk: Publishing House of the Novosibirsk University, 2002. - 459 p. - 2000 copies. - ISBN 5761505096 .
- Teyf V. B. et al. (2011). Nucleosomes in gene regulation: theoretical approaches. Molek. Biol. Volume 45, No. 6, p. 1-11. [one]
- Peter Tessarz & Tony Kouzarides (2014). Histone core modifications regulating nucleosome structure and dynamics . Nature Reviews Molecular Cell Biology 15, 703–708 DOI : 10.1038 / nrm3890
- Sheila S. Teves, Christopher M. Weber, Steven Henikoff (2014). Transcribing through the nucleosome. Trends in Biochemical Sciences, 39 (12), p577-586 DOI: https://dx.doi.org/10.1016/j.tibs.2014.10.004
- Thuy TM Ngo, Qiucen Zhang, Ruobo Zhou, Jaya G. Yodh, Taekjip Ha. (2015). Asymmetric Unwrapping of Nucleosomes under Tension Directed by DNA Local Flexibility . Cell, 160 (6): 1135–1144 DOI : 10.1016 / j.cell.2015.02.00.001