Conservation of deposition-related acetylation sites in newly synthesized histones H3 and H4.

Abstract

Newly synthesized histone H4 is deposited in a diacetylated isoform in a wide variety of organisms. In Tetrahymena a specific pair of residues, lysines 4 and 11, have been shown to undergo this modification in vivo. In this report, we demonstrate that the analogous residues, lysines 5 and 12, are acetylated in Drosophila and HeLa 114. These data strongly suggest that deposition-related acetylation sites in H4 have been highly, perhaps absolutely, conserved. In Tetrahymena and Drosophila newly synthesized histone H3 is also deposited in several modified forms. Using pulse-labeled H3 we have determined that, like H4, a specific, but distinct, subset of lysines is acetylated in these organisms. In Tetrahymena, lysines 9 and 14 are highly preferred sites of acetylation in new H3 while in Drosophila, lysines 14 and 23 are strongly preferred. No evidence has been obtained for acetylation of newly synthesized H3 in HeLa cells. Thus, although the pattern and sites of deposition-related acetylation appear to be highly conserved in H4, the same does not appear to be the case for histone H3.Modification of histones by acetylation of the E-amino group of specific lysine residues in the N-terminal domain of all four core histones is an active metabolic process whose exact function remains controversial. The primary focus of much current research is on how histone acetylation relates to the regulation of gene expression (1, 2). Less attention is being placed on understanding the biological function of depositionrelated acetylation, a reaction first described to affect specific histones during synthesis and deposition onto replicating chromatin (3,4).Biochemical analyses of deposition-related acetylation is hampered by the fact that only a fraction of the total histone is affected and once newly synthesized histone is deposited into nuclei, the pattern of acetylation is remodeled to fulfill transcription-related functions. In most systems, depositionrelated acetylation is witnessed only by administering a short pulse of label to preferentially label newly synthesized histones. Using this approach, numerous studies have reported that newly synthesized H4 is deposited as a modified isoform (3-9). This modification, although poorly understood, occurs in organisms ranging from protozoa to humans and thus appears to be highly conserved.In the ciliated protozoan Tetrahymena, deposition-related acetylation is particularly clear because of the separation between germ-line and somatic nuclei. Each vegetative cell contains a transcriptionally active, somatic macronucleus that governs the phenotype of the cell and a transcriptionally inert, germinal micronucleus that is responsible for genetic continuity. During conjugation, the sexual stage of the life cycle, essentially all of the newly synthesized H3 and H4 is selectively deposited into micronuclei; little if any new H3 or H4 is deposited into macronuclei (4). By stain and by label, histone extracted from these micronuclei is greatly enriched in diacetylated H4 and mono-and di...

Functional characterization of ATAD2 as a new cancer/testis factor and a predictor of poor prognosis in breast and lung cancers

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“…Most histone H4 acetylation is cell-cycle dependent and peaks at the replicative S phase, whereas global H3 acetylation levels do not seem to vary (Jasencakova et al, 2000). During chromatin assembly in S phase, the newly synthesized H4 molecules are acetylated at lysines 5 and 12 and, after H3/H4 deposition during DNA replication the H4 molecules are rapidly deacetylated (Sobel et al, 1995;Polo and Almouzni, 2006). Remarkably, this is a highly conserved phenomenon throughout eukaryotic evolution.…”

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