Weber V, Harata M, Hauser H, Wintersberger U
Department of Molecular Genetics, University of Vienna, Wien, Austria.
Mol Biol Cell. 1995 Oct;6(10):1263-70. doi: 10.1091/mbc.6.10.1263.
Actin-related proteins, a group of protein families that exhibit about 50% sequence identity among each other and to conventional actin, have been found in a variety of eukaryotic organisms. In the budding yeast Saccharomyces cerevisiae, genes for one conventional actin (ACT1) and for three actin-related proteins (ACT2, ACT3, and ACT5) are known. ACT3, which we recently discovered, is an essential gene coding for a polypeptide of 489 amino acids (Act3p), with a calculated molecular mass of 54.8 kDa. Besides its homology to conventional actin, Act3p possesses a domain exhibiting weak similarity to the chromosomal protein HMG-14 as well as a potential nuclear localization signal. An antiserum prepared against a specific segment of the ACT3 gene product recognizes a polypeptide band of approximately 55 kDa in yeast extract. Indirect immunofluorescence experiments with this antiserum revealed that Act3p is located in the nucleus. Nuclear staining was observed in all cells regardless of the stage of the cell cycle. Independently, immunoblotting experiments with subcellular fractions showed that Act3p is indeed highly enriched in the nuclear fraction. We suggest that Act3p is an essential constituent of yeast chromatin.
肌动蛋白相关蛋白是一类蛋白质家族，它们彼此之间以及与传统肌动蛋白具有约50%的序列同一性，已在多种真核生物中被发现。在出芽酵母酿酒酵母中，已知一种传统肌动蛋白（ACT1）和三种肌动蛋白相关蛋白（ACT2、ACT3和ACT5）的基因。我们最近发现的ACT3是一个必需基因，编码一种489个氨基酸的多肽（Act3p），计算分子量为54.8 kDa。除了与传统肌动蛋白具有同源性外，Act3p还拥有一个与染色体蛋白HMG - 14表现出弱相似性的结构域以及一个潜在的核定位信号。针对ACT3基因产物的特定片段制备的抗血清在酵母提取物中识别出一条约55 kDa的多肽带。用这种抗血清进行的间接免疫荧光实验表明，Act3p位于细胞核中。无论细胞周期处于哪个阶段，在所有细胞中均观察到核染色。独立地，用亚细胞组分进行的免疫印迹实验表明，Act3p确实在核组分中高度富集。我们认为Act3p是酵母染色质的重要组成部分。
