Leser G P, Fakan S, Martin T E
Department of Molecular Genetics and Cell Biology, University of Chicago, IL 60637.
Eur J Cell Biol. 1989 Dec;50(2):376-89.
The great majority of snRNP and hnRNP ribonucleoproteins have been shown to be confined to the nucleus except during periods of cell division. We have now determined the fine structure distribution of polypeptides associated with these RNP complexes during interphase and mitosis in mammalian tissue culture cells using immunoelectron microscopy. Many hnRNP antigens are found at the periphery of heterochromatin masses, known to be the sites of non-rRNP proteins initially surround areas of condensing chromatin and later become generally dispersed throughout the mitotic cell. The Sm protein antigens of snRNP complexes are found diffusely distributed in interphase nuclei as well as concentrated in fields of interchromatin granules (ICG). Proteins of snRNP complexes, unlike those of hnRNP, are associated with discernible cellular structures during mitosis. By prometaphase/metaphase, dense granular clusters are observed to contain a high concentration of snRNPs. These mitotic granule clusters (MGCs) are often in close proximity to chromosomal masses by late anaphase/telophase. The MGC structures are morphologically similar to interchromatin granule fields found in interphase nuclei. Furthermore, like interchromatin granules, they are sites of a high concentration of snRNP antigens and do not contain detectable hnRNP proteins or DNA.
绝大多数的核小核糖核蛋白（snRNP）和不均一核糖核蛋白（hnRNP）已被证明除了在细胞分裂期间外都局限于细胞核内。我们现在利用免疫电子显微镜确定了在哺乳动物组织培养细胞的间期和有丝分裂期间与这些核糖核蛋白复合物相关的多肽的精细结构分布。许多hnRNP抗原存在于异染色质块的周边，已知这些区域是非核糖体核糖核蛋白（rRNP）蛋白的位点，最初围绕着凝聚的染色质区域，随后在有丝分裂细胞中普遍分散。snRNP复合物的Sm蛋白抗原在间期核中呈弥散分布，同时也集中在染色质间颗粒（ICG）区域。与hnRNP不同，snRNP复合物的蛋白质在有丝分裂期间与可识别的细胞结构相关联。到前中期/中期时，观察到致密的颗粒簇含有高浓度的snRNP。这些有丝分裂颗粒簇（MGC）在后期/末期经常靠近染色体团块。MGC结构在形态上与间期核中发现的染色质间颗粒区域相似。此外，与染色质间颗粒一样，它们是高浓度snRNP抗原的位点，不含有可检测到的hnRNP蛋白或DNA。
