Prothymosin alpha (ProTalpha) is an abundant acidic nuclear protein that may be involved in cell proliferation. In our search for its cellular partners, we have recently found that ProTalpha binds to linker histone H1. We now provide further evidence for the physiological relevance of this interaction by immunoisolation of a histone H1-ProTalpha complex from NIH 3T3 cell extracts. A detailed an...

An additional hydrolysis site recognized by thrombin on histone H1 molecules was found. Snakes venom proteases from Agkistrodon rhodostoma, Bothrops marajoensis and Bothrops moojeni were further used for the analysis of H1 histones. The presence of the main cleavage site on H1 histone molecules has been established. This site is localized on main N-terminal thrombin peptide. The main venom prot...

A chromatin associated protein kinase was used to add 3 moles of phosphate to seryl side chains of 1 mole of histone H1. The DNA binding properties of this in vitro phosphorylated H1 were compared with those of unmodified H1. Considerably more radioactive superhelical DNA was retained on nitrocellulose filters at 20mM-40mM NaCl by phosphorylated H1 than by unmodified H1. However, zone velocity ...

A soybean histone-type protein kinase was used to prepare (32)P-labeled histone H1 as substrate for purification and characterization of a phosphoprotein phosphatase (EC 3.1.3.16) from soybean hypocotyls. The phosphatase has been purified 169-fold by ammonium sulfate fractionation, ethanol precipitation, and chromatography on Sephadex G-150, DEAE-Sephadex A-25 and Sephadex G-100. The activity o...

A gene encoding a protein that shows sequence similarity with the histone H1 family only was cloned in Ascobolus immersus. The deduced peptide sequence presents the characteristic three-domain structure of metazoan linker histones, with a central globular region, an N-terminal tail, and a long positively charged C-terminal tail. By constructing an artificial duplication of this gene, named H1, ...

Histone H1 is highly phosphorylated in mitotic HeLa cells, but is quickly dephosphorylated in vivo at the end of mitosis and in vitro following cell lysis. We show here that okadaic acid and microcystin-LR block the in vitro dephosphorylation of H1 and that they do so directly by inhibiting the histone H1 phosphatase rather than by some indirect mechanism. The concentrations of microcystin and ...

During cell division, condensation and resolution of chromosome arms and the assembly of a functional kinetochore at the centromere of each sister chromatid are essential steps for accurate segregation of the genome by the mitotic spindle, yet the contribution of individual chromatin proteins to these processes is poorly understood. We have investigated the role of embryonic linker histone H1 d...

The linker histone H1 generally participates in the establishment of chromatin structure. However, of the seven somatic H1 isotypes in humans some are also implicated in the regulation of local gene expression. Histone H1 isotype 4 (H1.4) represses transcription, and its lysine residue 26 (Lys(26)) was found to be important in this aspect. H1.4K26 is known to be methylated and acetylated in viv...

H1 histones are involved in the formation of higher order chromatin structures and in the modulation of gene expression. Changes in chromatin structure are a characteristic initial feature of apoptosis. We therefore have investigated the histone H1 pattern of the human leukemic cell line HL60 undergoing programmed cell death, as induced by topoisomerase I inhibition. Histone H1 proteins were is...