Johnson R M, Barrett P, Sommerville J
Eur J Biochem. 1984 Nov 2;144(3):503-8. doi: 10.1111/j.1432-1033.1984.tb08494.x.
At early stages of oogenesis in Xenopus laevis most of the ribosomal 5S RNA is complexed with three proteins to form two types of cytoplasmic RNP storage particle. A particle sedimenting at 42S contains 5S RNA and tRNA together with two proteins of Mr 48000 (P48) and Mr 43000 (P43) and a second particle sedimenting at 7S contains 5S RNA plus a protein of Mr 40000 (P40, also known as the transcription factor, TFIIIA). In this report we use antibodies monospecific for each protein to follow the movement of 5S RNA from nucleus to cytoplasm to nucleolus to cytoplasm and to determine the fate of each of the proteins that associate with 5S RNA during these transitions. Both P48 and P43 have roles additional to the formation of the 42S RNP storage particle; P48 is detected in the nucleus during early oogenesis and is cleaved to yield an Mr-33000 fragment that remains associated with 5S RNA that is excess to ribosome requirement during late oogenesis; P43 appears to be cleaved to yield fragments of Mr 28000 and 17000, the latter being present in ribosomal fractions. Apparently, there is no function for P40 in addition to those already described in transcription of 5S RNA genes and in storage of 5S RNA as a 7S RNP particle.
在非洲爪蟾卵子发生的早期阶段，大多数核糖体5S RNA与三种蛋白质复合，形成两种类型的细胞质核糖核蛋白（RNP）储存颗粒。沉降系数为42S的颗粒包含5S RNA和tRNA，以及分子量为48000的两种蛋白质（P48）和分子量为43000的蛋白质（P43）；沉降系数为7S的第二种颗粒包含5S RNA加上分子量为40000的蛋白质（P40，也称为转录因子TFIIIA）。在本报告中，我们使用对每种蛋白质具有单特异性的抗体来追踪5S RNA从细胞核到细胞质、再到核仁、然后回到细胞质的移动过程，并确定在这些转变过程中与5S RNA结合的每种蛋白质的命运。P48和P43在42S RNP储存颗粒形成之外还有其他作用；在卵子发生早期，P48在细胞核中被检测到，并被切割产生一个分子量为33000的片段，该片段在卵子发生后期仍与超过核糖体需求的5S RNA结合；P43似乎被切割产生分子量为28000和17000的片段，后者存在于核糖体组分中。显然，除了已经描述的在5S RNA基因转录以及作为7S RNP颗粒储存5S RNA方面的功能外，P40没有其他功能。
