DNA replication and H5 histone exchange during reactivation of chick erythrocyte nuclei in heterokaryons

ABSTRACT The eukaryotic genome is packaged together with histone proteins into chromatin following DNA replication. Recent studies have shown that histones can also be assembled into chromatin independently of DNA replication and that this dynamic exchange of histones may be biased toward sites undergoing transcription. Here we show that epitope-tagged histone H4 can be incorporated into nucleosomes throughout the budding yeast (Saccharomyces cerevisiae) genome regardless of the phase of the cell cycle, the transcriptional status, or silencing of the region. Direct comparisons reveal that the amount of histone incorporation that occurs in G1-arrested cells is similar to that occurring in cells undergoing DNA replication. Additionally, we show that this histone incorporation is not dependent on the histone H3/H4 chaperones CAF-1, Asf1, and Hir1 individually. This study demonstrates that DNA replication and transcription are not necessary prerequisites for histone exchange in budding yeast, indicating that chromatin is more dynamic than previously thought.

Download Full-text

A novel histone exchange factor, protein phosphatase 2Cγ, mediates the exchange and dephosphorylation of H2A–H2B

The Journal of Cell Biology ◽

10.1083/jcb.200608001 ◽

2006 ◽

Vol 175 (3) ◽

pp. 389-400 ◽

Cited By ~ 51

Author(s):

Hiroshi Kimura ◽

Nanako Takizawa ◽

Eric Allemand ◽

Tetsuya Hori ◽

Francisco J. Iborra ◽

...

Keyword(s):

Dna Replication ◽

Protein Phosphatase ◽

Fluorescent Protein ◽

Histone Variants ◽

Permeabilized Cells ◽

Cellular Factors ◽

Core Histones ◽

Green Fluorescent ◽

Histone Exchange

In eukaryotic nuclei, DNA is wrapped around a protein octamer composed of the core histones H2A, H2B, H3, and H4, forming nucleosomes as the fundamental units of chromatin. The modification and deposition of specific histone variants play key roles in chromatin function. In this study, we established an in vitro system based on permeabilized cells that allows the assembly and exchange of histones in situ. H2A and H2B, each tagged with green fluorescent protein (GFP), are incorporated into euchromatin by exchange independently of DNA replication, and H3.1-GFP is assembled into replicated chromatin, as found in living cells. By purifying the cellular factors that assist in the incorporation of H2A–H2B, we identified protein phosphatase (PP) 2C γ subtype (PP2Cγ/PPM1G) as a histone chaperone that binds to and dephosphorylates H2A–H2B. The disruption of PP2Cγ in chicken DT40 cells increased the sensitivity to caffeine, a reagent that disturbs DNA replication and damage checkpoints, suggesting the involvement of PP2Cγ-mediated histone dephosphorylation and exchange in damage response or checkpoint recovery in higher eukaryotes.

Download Full-text

Replication of Bacteriophage 186 DNA

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010009422x ◽

1972 ◽

Vol 30 ◽

pp. 194-195

Author(s):

Dhruba K. Chattoraj ◽

Ross B. Inman

Keyword(s):

Electron Microscopy ◽

Dna Replication ◽

Frame Of Reference ◽

Dna Molecules ◽

E Coli ◽

Phage Dna ◽

Partial Denaturation

Electron microscopy of replicating intermediates has been quite useful in understanding the mechanism of DNA replication in DNA molecules of bacteriophage, mitochondria and plasmids. The use of partial denaturation mapping has made the tool more powerful by providing a frame of reference by which the position of the replicating forks in bacteriophage DNA can be determined on the circular replicating molecules. This provided an easy means to find the origin and direction of replication in λ and P2 phage DNA molecules. DNA of temperate E. coli phage 186 was found to have an unique denaturation map and encouraged us to look into its mode of replication.

Download Full-text