Histone H1 is highly phosphorylated in transcriptionally active, amitotic macronuclei of Tetrahymena during vegetative growth. However, the level of H1 phosphorylation changes dramatically in response to different physiological conditions. H1 is hyperphosphorylated in response to heat shock and during prezygotic stages of conjugation. Conversely, H1 is largely dephosphorylated during prolonged ...

The binding of H1 (and H5) to nucleosome core particles was demonstrated by separating mononucleosomes according to their DNA size on acrylamide gels containing high molarity urea. The presence of urea causes a redistribution of H1 so that it associates with some particles of all linker lengths, including no linker. When the urea is removed the H1 remains associated with particles of all DNA si...

Posttranslational modifications and remodeling of nucleosomes are critical factors in the regulation of transcription. Higher-order folding of chromatin also is likely to contribute to the control of gene expression, but the absence of a detailed description of the structure of the chromatin fiber has impaired progress in this area. Mammalian somatic cells contain a set of H1 linker-histone sub...

TopoisomeraseII (Topo II) is a major component of chromosomal scaffolds and essential for mitotic chromosome condensation, but the mechanism of this action remains unknown. Here, we used an in vitro chromatin reconstitution system in combination with atomic force and fluorescence microscopic analyses to determine how Topo II affects chromosomal structure. Topo II bound to bare DNA and clamped t...

Linker histones of the H1 family are among the most abundant components of chromatin. In this issue of Cell, the effect of H1 downregulation on gene expression is examined. Although a 50% reduction of histone H1 levels in embryonic stem cells affects chromatin structure globally, the expression of very few genes is altered. Intriguingly, this study reveals a new link between H1 and DNA methylat...

DNA double-strand breaks (DSBs) induced in the genome of higher eukaryotes by ionizing radiation (IR) are predominantly removed by two pathways of non-homologous end-joining (NHEJ) termed D-NHEJ and B-NHEJ. While D-NHEJ depends on the activities of the DNA-dependent protein kinase (DNA-PK) and DNA ligase IV/XRCC4/XLF, B-NHEJ utilizes, at least partly, DNA ligase III/XRCC1 and PARP-1. Using in v...

Chemically induced differentiation of murine erythroleukemia cells is a multistep process involving a precommitment period in which exposure to inducer leads to cells that are irreversibly committed to terminal differentiation. Certain changes in the expression of cellular proto-oncogenes are an important feature of the precommitment phase. We have identified two H1 histone genes that are rapid...

In virtually all eukaryotic organisms, linker DNA between nucleosomes is associated with a histone termed linker histone or histone H1. In Saccharomyces cerevisiae, HHO1 encodes a putative linker histone with very significant homology to histone H1. The encoded protein is expressed in the nucleus, but has not been shown to affect global chromatin structure, nor has its deletion shown any detect...

We have used a combination of kinetic measurements and targeted mutations to show that the C-terminal domain is required for high-affinity binding of histone H1 to chromatin, and phosphorylations can disrupt binding by affecting the secondary structure of the C terminus. By measuring the fluorescence recovery after photo-bleaching profiles of green fluorescent protein-histone H1 proteins in liv...