Lusser A, Brosch G, López-Rodas G, Loidl P
Department of Microbiology, University of Innsbruck, Medical School, Austria.
Eur J Cell Biol. 1997 Sep;74(1):102-10.
The dynamic state of histone acetylation is maintained by histone acetyltransferases (HATs) and deacetylases. Cellular fractionation of plasmodia of Physarum polycephalum and partial purification of subcellular fractions by chromatography revealed the existence of a cytoplasmic B-type and four nuclear A-type HATs. The cytoplasmic B-enzyme was highly specific for histone H4, causing di-acetylation of H4 in vitro. The nuclear enzymes (HAT-A1 to HAT-A4) accepted all core histones as substrates, but differed by the preference for certain histone species. Enzymes were analyzed during the naturally synchronous cell cycle of macroplasmodia. Each of the enzymes had its individual cell cycle activity pattern, indicating diverse functions in nuclear metabolism. When growing plasmodia were induced to undergo differentiation into dormant sclerotia, an additional enzyme (HAT-AS) appeared at a late stage of sclerotization which correlated with differentiation-specific histone synthesis and acetylation in the absence of DNA replication. When dormant sclerotia were induced to reenter the cell cycle, a further enzyme form (HAT-AG) appeared during a short time period prior to the first post-germination mitosis. This enzyme had a strong preference for H2B, correlating with the overproportional in vivo acetate incorporation in H2B. Both differentiation-associated HATs were undetectable in growing plasmodia. The results demonstrate that different functions of core histone acetylation are based on multiple enzyme forms that are independently regulated during the cell cycle. Transitions from one developmental stage into another are accompanied by specific enzyme forms. With respect to recent data in the literature it may be assumed that these HAT-forms are subunits of a HAT-complex whose composition changes during the cell cycle and differentiation.
组蛋白乙酰化的动态状态由组蛋白乙酰转移酶（HATs）和去乙酰化酶维持。对多头绒泡菌的原质团进行细胞分级分离，并通过色谱法对亚细胞级分进行部分纯化，结果显示存在一种细胞质B型和四种核A型HATs。细胞质B酶对组蛋白H4具有高度特异性，可在体外使H4发生双乙酰化。核酶（HAT-A1至HAT-A4）以所有核心组蛋白为底物，但对某些组蛋白种类的偏好有所不同。在大原质团自然同步的细胞周期中对这些酶进行了分析。每种酶都有其独特的细胞周期活性模式，表明它们在核代谢中具有多种功能。当生长中的原质团被诱导分化为休眠菌核时，在菌核化后期出现了一种额外的酶（HAT-AS），这与分化特异性组蛋白合成和在无DNA复制情况下的乙酰化相关。当休眠菌核被诱导重新进入细胞周期时，在萌发后的第一次有丝分裂之前的短时间内出现了另一种酶形式（HAT-AG）。这种酶对H2B有强烈偏好，这与体内H2B中过量的乙酸掺入相关。在生长中的原质团中均未检测到这两种与分化相关的HATs。结果表明，核心组蛋白乙酰化的不同功能基于多种酶形式，这些酶形式在细胞周期中受到独立调节。从一个发育阶段向另一个发育阶段的转变伴随着特定的酶形式。根据文献中的最新数据，可以推测这些HAT形式是HAT复合物的亚基，其组成在细胞周期和分化过程中会发生变化。
