DNA wrapping in nucleosomes. The linking number problem re-examined

Area of Science:

• Molecular Biology
• Biochemistry
• Genetics

Background:

• Chromatin structure is crucial for DNA regulation.
• The linking number problem describes discrepancies in DNA linking number in chromatin models.
• Understanding histone-DNA interactions is key to resolving this problem.

Purpose of the Study:

• To investigate the effect of histone H1 and H5 on DNA linking number in vitro.
• To explore potential solutions to the chromatin linking number problem.

Main Methods:

• In vitro assembly of chromatin using SV40 DNA and core histones.
• Incubation with topoisomerase I to relax supercoils.
• Addition of histones H1 + H5 at specific ionic strength and with polyglutamic acid.

Main Results:

• Histones H1 + H5 increased the magnitude of DNA linking number change in chromatin.
• No change in linking number was observed for protein-free DNA.
• The observed change was not due to an increased nucleosome density.

Conclusions:

• Histone H1 and H5 influence DNA topology in chromatin.
• These findings provide a potential resolution to the linking number problem in chromatin structure.