Study of in vitro phosphorylation of histones H3, H4 and of the non-acetylated and acetylated tetramers (H3–H4)2

Granyer Giralt, JosepPrimer pla de l'obra. Coneguda com el Vedell o el Toro, en actitud de meditar. Mesura 2,42 x 0,62 x 0,76 metres i és de bronze

Acetylation of core histones in response to HDAC inhibitors is diminished in mitotic HeLa cells

Histone acetylation is a key modification that regulates chromatin accessibility. Here we show that treatment with butyrate or other histone deacetylase (HDAC) inhibitors does not induce histone hyperacetylation in metaphase-arrested HeLa cells. When compared to similarly treated interphase cells, acetylation levels are significantly decreased in all four core histones and at all individual sites examined. However, the extent of the decrease varies, ranging from only slight reduction at H3K23 and H4K12 to no acetylation at H3K27 and barely detectable acetylation at H4K16. Our results show that the bulk effect is not due to increased or butyrate-insensitive HDAC activity, though these factors may play a role with some individual sites. We conclude that the lack of histone acetylation during mitosis is primarily due to changes in histone acetyltransferases (HATs) or changes in chromatin. The effects of protein phosphatase inhibitors on histone acetylation in cell lysates suggest that the reduced ability of histones to become acetylated in mitotic cells depends on protein phosphorylation

Site and role of the N-terminal fragment of the nucleosomal core histones in their binding to deoxyribonucleic acid as determined by vibrational spectroscopy

The site and role of the binding of the 1-53 N-terminal part of H4 on DNA have been studied by optical spectroscopy. The structure of the 1-53 H4 fragment determined by vacuum ultraviolet circular dichroism and infrared spectroscopy is essentially aperiodic. The site of the interacion between the fragment and free DNA is localized by Raman laser spectroscopy in the small groove of the DNA, similar to the interaction site of the whole histone with DNA in nucleosomes. Infrared linear dichroism measurements show that the two 1-53 and 54-102 H4 fragments play a very important role in the histone-DNA interactions, but the roles are extremely different: the N-terminal part of the histone remains effectless on the DNA conformational flexibility and it is proposed that the structurally important interaction occurs between the globular part of the histone and the DNA. The N-terminal fragment appears to be responsible for finding the correct place on the DNA of the nucleosomal core particles