Loidl P, Gröbner P
Nucleic Acids Res. 1986 May 12;14(9):3745-62. doi: 10.1093/nar/14.9.3745.
Plasmodia of Physarum polycephalum can be induced to differentiate into dormant spherules: DNA-, RNA- and protein-synthesis cease during this process. Analysis of the histone H4 acetylation during spherulation revealed no significant changes of the relative acetate content and percentage of acetylated H4 subspecies. This result does not support a close correlation of histone acetylation and transcriptional activity. Posttranslational incorporation of 3H-acetate into core histones decreased rapidly after start of spherulation. However, acetate incorporation increased significantly at a late stage of spherulation (30 h). To elucidate the role of this elevated acetate incorporation we followed histone synthesis during spherulation. Histone synthesis decreased upon induction of differentiation and stopped after 12 h. After 38 h of spherulation histone synthesis again occurred in the absence of DNA synthesis. The peak of acetate incorporation into core histones clearly preceded this late histone synthesis, indicating acetylation of preexisting histones. We suggest, that this acetate incorporation is part of the mechanism, by which preexisting histones are replaced by newly synthesized histones. Pulse treatment with actinomycin D or cycloheximide during spherulation suggested, that the observed histone synthesis is essential for the germination of spherules. Obviously, new histones have to be synthesized for the coordinate course of the differentiation program.
在此过程中，DNA、RNA和蛋白质合成停止。对小球形成过程中组蛋白H4乙酰化的分析表明，相对乙酸含量和乙酰化H4亚型的百分比没有显著变化。这一结果不支持组蛋白乙酰化与转录活性密切相关的观点。在小球形成开始后，3H-乙酸向核心组蛋白的翻译后掺入迅速减少。然而，在小球形成后期（30小时），乙酸掺入显著增加。为了阐明这种乙酸掺入增加的作用，我们在小球形成过程中跟踪了组蛋白的合成。诱导分化后组蛋白合成减少，并在12小时后停止。在小球形成38小时后，在没有DNA合成的情况下再次出现组蛋白合成。核心组蛋白乙酸掺入的峰值明显先于这种后期组蛋白合成，表明预先存在的组蛋白发生了乙酰化。我们认为，这种乙酸掺入是预先存在的组蛋白被新合成的组蛋白取代的机制的一部分。在小球形成过程中用放线菌素D或环己酰亚胺进行脉冲处理表明，观察到的组蛋白合成对于小球的萌发至关重要。显然，为了分化程序的协调进行，必须合成新的组蛋白。
