Histone acetylation in conjugating Tetrahymena thermophila [published erratum appears in J Cell Biol 1989 Dec;109(6 Pt 1):3214-7]

Abstract

Abstract. We have monitored histone acetylation during conjugation of the ciliated protozoan Tetrahymena thermophila using antibodies against the tetraacetylated form of H4 histone (Pfeffer, U., N. Ferrari, and G. Vidali. 1986. J. Biol. Chem. 261:2496-2498. During meiosis, the three prezygotic divisions, fertilization, and the first postzygotic division, micronuclei, do not contain highly acetylated forms of H4 histone. However, after the second postzygotic division, when anteriorly located micronuclei begin to develop into new macronuclei, they are strongly stained by the anti-tetraacetylated H4 histone antibody. In the old macronucleus, histones are actively deacetylated when it has ceased to transcribe but before it is eliminated. Histone acetylation processes analyzed here appear to be correlated to the commitment to transcription rather than to the transcription process itself. This is in good correlation with evidence we have obtained in chick erythrocyte nuclei during reactivation upon fusion with mammalian cells (Pfeffer, U., N. Ferrari, E Tosetti, and G. Vidali. 1988. Exp. Cell Res. 178:25-30). Furthermore, it becomes clear from our data that histone acetylation occurs in close correlation to the position of nuclei within the cytoplasm of T. thermophila.Mechanisms that control differential histone acetylation and deacetylation are discussed.S INCE the original observation, histone acetylation has been correlated to transcription and considerable evidence has accumulated indicating that this reversible postsynthetic modification of lysine residues in the aminoterminal portion of core histones plays a key role in the regulation of gene expression (for a review see reference 2).Different methods have been developed to fractionate chromatin depending on its transcriptional activity and accordingly, it has been found that fractions containing actively transcribed genes were enriched in highly acetylated histones (1,17,33). Recent analyses using anti-acetyl-lysine antibodies have established that a given gene is associated with highly acetylated histones when it is transcribed (23), although it cannot be ruled out that genes competent to be transcribed, but inactive at the moment of analysis, may also contain acetylated histones.Nucleosomes undergo reversible conformational changes during transcriptional activation (10, 32), histones are absent from promoter sequences of active genes (25), nucleosomes inhibit initiation of transcription but do not inhibit elongation of initiated transcripts (27, 28) and at least H4 histone is retained on a highly transcribed gene (35). The contact points between nucleosomal DNA and H4 histone have been analyzed and a highly basic cluster in the amino-terminal portion has been shown to be involved in sharp bending of the DNA double helix (18). Interestingly, this cluster encompasses lysine at position 16 which is the first to be acetylated in vivo in calf thymus (15) and, moreover, this region is in close contact to a site 55-65 bp from the end of the nucleosomal DNA, which ...

N6-adenine DNA methylation is associated with the linker DNA of H2A.Z-containing well-positioned nucleosomes in Pol II-transcribed genes in Tetrahymena

“…6mA is eventually established in the latter by de novo deposition (Figure 1C ) ( 19 , 20 ). Intriguingly, we found that 6mA was not detected in the early developing new MAC (Figure 1C ), even though transcription and transcription-associated epigenetic marks—including H2A.Z and histone hyper-acetylation ( Supplementary Figure S4 )—are already present in abundance ( 44 , 45 ). We only detected 6mA signals in the new MAC several hours later at the last stage of conjugation, in which there were two new MACs and one new MIC, with the old MAC having been reabsorbed (Figure 1C ).…”

The Transmembrane Protein Semi1 Positions Gamete Nuclei for Reciprocal Fertilization in Tetrahymena

“…In fact, in the selected hMIC histone H3 is acetylated at several lysine residues (Akematsu et al, 2017) other than K56 (Figure 3A). Acetylation of histone H3 at these sites is strongly enriched in euchromatin (Wang et al., 2008, Tie et al., 2009) and also characteristic of the active MAC (Chicoine and Allis, 1986, Pfeffer et al., 1989). This change may also be critical to protect the selected hMIC from autophagy, which eliminates the unselected hMICs (Liu and Yao, 2012).…”