Kloetzel P M, Whitfield W, Sommerville J
Nucleic Acids Res. 1981 Feb 11;9(3):605-21. doi: 10.1093/nar/9.3.605.
Previtellogenic oocytes of Triturus cristatus accumulate a free cytoplasmic RNP which sediments at 40S and contain 5S RNA and tRNA in association with two proteins of MW 45,000 and 39,000 daltons (P45 and P39). The 40S particle has a buoyant density of 1.53 g . cm-3 in CsCl and consists of four identical RNP subunits. Each monomeric subunit contains one molecule of 5S RNA, three molecules of tRNA, two molecules of P45 and one molecule of P39. The 40S particle can be completely dissociated by SDS treatment into its individual components, and the subunits, and even the complete 40S particle, can be reformed by removal of SDS in the presence of 0.2 M NaCl. RNA/protein binding experiments with isolated components, and analysis of reformed RNP complexes in CsCl gradients, demonstrate that the stable interactions are: 5S RNA/P45, 3(tRNA)/P45, 5S RNA/P39 and 5S RNA/P45/P39. Immunological studies show that P45 has also a nuclear location and may bind to the 5S RNA transcript in the chromatin, whereas P39 is predominantly cytoplasmic and is possibly related to proteins associated with 5S RNA in the ribosomal 60S subunit. It is suggested that the 40S RNP particle not only stores 5S RNA and tRNA but also provides a means for the exchange of the 5S RNA transcript binding protein (P45) for the 5S RNA ribosome associated protein (P39).
雄性蝾螈的卵黄发生前卵母细胞积累了一种游离的细胞质核糖核蛋白（RNP），其沉降系数为40S，含有5S RNA和tRNA，并与分子量分别为45,000和39,000道尔顿的两种蛋白质（P45和P39）结合。40S颗粒在CsCl中的浮力密度为1.53 g·cm-3，由四个相同的RNP亚基组成。每个单体亚基包含一个5S RNA分子、三个tRNA分子、两个P45分子和一个P39分子。40S颗粒经SDS处理后可完全解离成其各个组分，在0.2 M NaCl存在下除去SDS时，亚基甚至完整的40S颗粒都可重新形成。用分离的组分进行的RNA/蛋白质结合实验以及对CsCl梯度中重新形成的RNP复合物的分析表明，稳定的相互作用为：5S RNA/P45、3（tRNA）/P45、5S RNA/P39和5S RNA/P45/P39。免疫学研究表明，P45也定位于细胞核，可能与染色质中的5S RNA转录本结合，而P39主要位于细胞质中，可能与核糖体60S亚基中与5S RNA相关的蛋白质有关。有人提出，40S RNP颗粒不仅储存5S RNA和tRNA，还为将5S RNA转录本结合蛋白（P45）交换为5S RNA核糖体相关蛋白（P39）提供了一种方式。
