Abstract. Salt extracts prepared from purified micronuclei and the cytoplasm of growing Tetrahymena contain a histone acetylase (also referred to as histone acetyltransferase) activity which is highly specific for H4 when tested as a free historic. With both extracts, H4 is acetylated first at position 4 (monoacetylated) or positions 4 and I1 (diacetylated), sites diagnostic of deposition-related acetylation of newly synthesized H4 in vivo. As the concentration of cytosolic extract is decreased in the in vitro reactions, acetylation of H3 is also observed. Neither activity acetylates histone in a chromatin form.These activities are distinct from a macronuclear acetylase which acetylates H3 and H4 (macro-or micronuclear) equally well as free histones and which acetylates all four core histones when mononucleosomes are used as substrate. As well, the micronuclear and cytoplasmic activities give similar thermalinactivation profiles which are different from that of the macronuclear activity. In situ enzyme assays demonstrate a macronuclear-specific activity which acetylates endogenous macronuclear chromatin and an independent micronuclear-cytosolic activity which is able to act upon exogenously added free H4. These results argue strongly that an identical acetylase is responsible for the micronuclear and cytoplasmic activity which is either modified or altogether distinct from that in macronuclei.TUDIES in vivo have demonstrated that at least two general systems of historic acetylation exist in the ciliated protozoan, Tetrahymena. One system, which we will refer to as "transcription-related" acetylation, is postsynthetic and affects all of the inner (non-H1) histones in transcriptionally active macronuclei. This system does not appear to exist in transcriptionally inactive micronuclei (Vavra et al., 1982;. In contrast, a second system, which we will refer to as "deposition/replicationrelated" acetylation, requires protein synthesis and affects histones H3 and H4, regardless of whether they are destined for macro-or micronuclei (Allis et al., 1985).In an attempt to understand further the biological function of histone acetylation as it relates to both transcription and chromatin assembly, we have begun to analyze the enzyme system(s) responsible for carrying out histone acetylation in Tetrahymena. Recently, we described results which suggest that a single histone acetylase (also referred to as histone acetyltransferase) extracted from purified macronuclei catalyzes both transcription-and deposition-related acetylation, depending upon the substrate used in the reaction (Chicoine et al., 1987). When mononucleosomes are used as a substrate for this activity, all four core histones are acetylated in a manner indistinguishable from postsynthetic transcriptionrelated acetylation. However, when free histories are used as a substrate, the same activity acetylates mainly H3 and H4 in a manner surprisingly similar to deposition/replicationrelated acetylation.Although having both of these biologically important acetylations car...
With decreasing blood loss, safe but stringent criteria for transfusion and improved safety of the blood supply, autologous donation is an inefficient method to lower the slight risk of complications following homologous transfusion during radical prostatectomy.
Genetic and biochemical studies have shown that cdc2 protein kinase plays a pivotal role in a highly conserved mechanism controlling the entry of cells into mitosis. It is generally believed that one function of cdc2 kinase is to phosphorylate histone H1 which in turn promotes mitotic chromosome condensation. However, direct evidence linking H1 phosphorylation to mitotic chromatin condensation is limited and the exact cellular function(s) of H1 phosphorylation remains unclear. In this study, we show that mammalian cdc2 kinase phosphorylates H1 from the amitotic macronucleus of Tetrahymena with remarkable fidelity. Furthermore, we demonstrate that macronuclei from Tetrahymena contain a growth‐associated H1 kinase activity which closely resembles cdc2 kinase from other eukaryotes. Using polyclonal antibodies raised against yeast p34cdc2, we have detected a 36 kd immunoactive polypeptide in macronuclei which binds to Suc1 (p13)‐coated beads and closely follows H1 kinase activity. Since macronuclei divide without mitotic chromosome condensation, these data demonstrate that H1 phosphorylation by cdc2 kinase may be necessary, but is not sufficient to promote mitotic chromatin condensation. The fact that an activity which strongly resembles mammalian cdc2 kinase is active during cell growth in a nucleus which does not undergo mitosis and chromosome condensation suggests that other factors are needed for a true mitotic division to occur. These data also reinforce the notion that H1 phosphorylation has important functions outside mitosis both in Tetrahymena and in mammalian cells.
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