This results in a strong hydrogen bond that has the nearly optimum N…O distance of 2.8 A.

TLS Online TPP Program

#Id: 395

#Unit 2. Cellular Organization

Relatively short length (30 bp) of DNA bound by H2A.H2B dimers is not sufficient to prepare the DNA for H3.H4 tetramer binding.

TLS Online TPP Program

#Id: 396

#Unit 2. Cellular Organization

Each nucleosome added to a covalently closed circular template changes the linking number of the associated DNA by approximately –1.2.

TLS Online TPP Program

#Id: 397

#Unit 2. Cellular Organization

Nucleosomal DNA wraps around the histone protein 1.65 times, so create a writhe of –1.65 and so DLk should be -1.65. But when the change in linking number associated with each nucleosome was measured, the number was lower than this, approximately –1.2 for each nucleosome added. This discrepancy is referred to as the “Nucleosome Linking Number paradox,”

TLS Online TPP Program

#Id: 398

#Unit 2. Cellular Organization

Modification of histones is associated with replication and transcription, and specific modifications also facilitate DNA repair.

TLS Online TPP Program

#Id: 399

#Unit 2. Cellular Organization

Variants have been identified for all core histones except histone H4.

TLS Online TPP Program

#Id: 400

#Unit 2. Cellular Organization

MacroH2A is nearly three times larger than conventional H2A, and contains a large C-terminal tail that is not related to any other histone.