Hamm J, Mattaj I W
EMBL Heidelberg, FRG.
EMBO J. 1989 Dec 20;8(13):4179-87. doi: 10.1002/j.1460-2075.1989.tb08603.x.
The particle state of U snRNPs was analyzed in oocytes, eggs, embryos and testes from Xenopus laevis. In each case both the relative abundance and the composition of some U snRNPs were found to differ from that of somatic cells. U2 and U6 snRNPs were the most prominent U snRNPs in germ cells and early embryos. In particular, the concentration of U6 snRNA was 10-20 times higher than that of U4 snRNA. Most of the U6 snRNA was not associated with U4 snRNA and migrated on sucrose gradients as a U6 snRNP. The structure of this novel U snRNP was analyzed. A single protein of 50 kd was copurified with U6 snRNPs by a combination of gradient fractionation, immunodepletion with anti-Sm antibodies and immunoprecipitation with anti-6-methyl adenosine antibodies. Although the U6 snRNP did not contain Sm proteins it migrated into the nucleus when U6 snRNA was injected into the cytoplasm of oocytes. Two U6 snRNA elements have been identified. The first is essential for nuclear migration in oocytes, but not for the formation of U4/6 snRNPs in vitro and might be the binding site of a U6-specific protein. The second element was required for interaction with U4 snRNPs but not for nuclear targeting.
对非洲爪蟾卵母细胞、卵子、胚胎和睾丸中的U小核核糖核蛋白颗粒状态进行了分析。在每种情况下，都发现一些U小核核糖核蛋白的相对丰度和组成与体细胞不同。U2和U6小核核糖核蛋白是生殖细胞和早期胚胎中最主要的U小核核糖核蛋白。特别是，U6小核RNA的浓度比U4小核RNA高10到20倍。大多数U6小核RNA不与U4小核RNA结合，并以U6小核核糖核蛋白的形式在蔗糖梯度上迁移。对这种新型U小核核糖核蛋白的结构进行了分析。通过梯度分级分离、抗Sm抗体免疫去除和抗6-甲基腺苷抗体免疫沉淀相结合的方法，一种50kd的单一蛋白质与U6小核核糖核蛋白共纯化。尽管U6小核核糖核蛋白不含Sm蛋白，但当将U6小核RNA注入卵母细胞的细胞质中时，它会迁移到细胞核中。已鉴定出两个U6小核RNA元件。第一个元件对卵母细胞中的核迁移至关重要，但对体外U4/6小核核糖核蛋白的形成不是必需的，可能是一种U6特异性蛋白的结合位点。第二个元件是与U4小核核糖核蛋白相互作用所必需的，但对核靶向不是必需的。
