AI Article Synopsis

  • In sperm cells, protamine replaces histones to compact DNA significantly more than in other cells, resulting in extreme DNA condensing.
  • Using confocal microscopy and optical tweezers, researchers found that increasing protamine levels led to greater compaction of λ-DNA, forming resistant tangles and reducing its length by up to 40%.
  • The study suggests that protamine interacts with DNA bases through hydrogen bonds, impacting both local and overall chromatin organization, which may contribute to transcriptional silencing in sperm.

Article Abstract

In sperm cells, protamine replaces histones to compact DNA 10-20 times more than in somatic cells. To characterize the extreme compaction, we employed confocal microscopy and optical tweezers to determine the conformations and stability of protamine-bound λ-DNA. Confocal images show increasing compaction of λ-DNA at increasing protamine concentration. In the presence of protamine, single λ-DNA molecules form tangles that withstand forces strong enough (∼55 pN) for strand separation and shorten the contour length by up to 40% even at high forces, as well as bends and loops that rupture at 10-40 pN forces. Strand separation nucleates tangles, implicating protamine interactions with DNA bases. Molecular dynamics simulations show that Arg sidechains of protamine each form hydrogen bonds with multiple bases, frequently in the form of a wedge between the two strands of DNA. Protamine may participate in both local and higher-order chromatin organization, leading to extreme compaction and global transcription silencing.

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Source
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC11540724PMC
http://dx.doi.org/10.1021/jacs.4c12468DOI Listing

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