Histone chaperones facilitate DNA replication and repair by promoting chromatin assembly, disassembly and histone exchange. Following histones synthesis and nucleosome assembly, the histones undergo posttranslational modification by different enzymes and are deposited onto chromatins by various histone chaperones. In Tetrahymena thermophila, histones from macronucleus (MAC) and micronucleus (MIC) have been comprehensively investigated, but the function of histone chaperones remains unclear. Histone chaperone Nrp1 in Tetrahymena contains four conserved tetratricopepeptide repeat (TPR) domains and one C-terminal nuclear localization signal. TPR2 is typically interrupted by a large acidic motif. Immunofluorescence staining showed that Nrp1 is located in the MAC and MICs, but disappeared in the apoptotic parental MAC and the degraded MICs during the conjugation stage. Nrp1 was also colocalized with α-tubulin around the spindle structure. NRP1 knockdown inhibited cellular proliferation and led to the loss of chromosome, abnormal macronuclear amitosis, and disorganized micronuclear mitosis during the vegetative growth stage. During sexual developmental stage, the gametic nuclei failed to be selected and abnormally degraded in NRP1 knockdown mutants. Affinity purification combined with mass spectrometry analysis indicated that Nrp1 is co-purified with core histones, heat shock proteins, histone chaperones, and DNA damage repair proteins. The physical direct interaction of Nrp1 and Asf1 was also confirmed by pull-down analysis in vitro. The results show that histone chaperone Nrp1 is involved in micronuclear mitosis and macronuclear amitosis in the vegetative growth stage and maintains gametic nuclei formation during the sexual developmental stage. Nrp1 is required for chromatin stability and nuclear division in Tetrahymena thermophila.

中文翻译：

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组蛋白伴侣 Nrp1 是嗜热四膜虫染色质稳定性和核分裂所必需的

组蛋白伴侣通过促进染色质组装、分解和组蛋白交换来促进 DNA 复制和修复。在组蛋白合成和核小体组装之后，组蛋白通过不同的酶进行翻译后修饰，并通过各种组蛋白伴侣沉积在染色质上。在嗜热四膜虫中，来自大核（MAC）和微核（MIC）的组蛋白已被全面研究，但组蛋白伴侣的功能仍不清楚。四膜虫中的组蛋白伴侣 Nrp1 包含四个保守的四肽重复 (TPR) 结构域和一个 C 末端核定位信号。TPR2 通常被一个大的酸性基序打断。免疫荧光染色显示 Nrp1 位于 MAC 和 MICs 中，但在结合阶段在凋亡亲代 MAC 和降解的 MIC 中消失。Nrp1 也与纺锤体结构周围的α-微管蛋白共定位。NRP1 敲低抑制细胞增殖并导致营养生长阶段的染色体丢失、异常的大核有丝分裂和杂乱无章的微核有丝分裂。在性发育阶段，配子核未能被选择并在 NRP1 敲低突变体中异常降解。亲和纯化结合质谱分析表明，Nrp1 与核心组蛋白、热休克蛋白、组蛋白伴侣和 DNA 损伤修复蛋白共同纯化。Nrp1 和 Asf1 的物理直接相互作用也通过体外下拉分析得到证实。结果表明，组蛋白伴侣Nrp1在营养生长阶段参与微核有丝分裂和大核无丝分裂，在有性发育阶段维持配子核的形成。Nrp1 是嗜热四膜虫染色质稳定性和核分裂所必需的。