Lehner C F, Kurer V, Eppenberger H M, Nigg E A
J Biol Chem. 1986 Oct 5;261(28):13293-301.
The nuclear lamina, a structure closely apposed to the inner nuclear membrane, is believed to provide a framework important for nuclear envelope integrity and interphase chromatin organization. So far, in mammalian and avian species three major constituents of the lamina, lamins A, B, and C, have been identified. These proteins migrate to characteristic positions on two-dimensional gels, lamin B being more acidic than lamins A and C. Here, we show that the composition of the nuclear lamina in avian and mammalian cells is more complex than previously assumed. When analyzed on two-dimensional gels, the major 66-kDa chicken "lamin B" protein can readily be identified. However, an additional 68-kDa protein migrates to a similarly acidic position. Based on the following evidence, both proteins can be considered as two distinct members of the lamin protein family. First, peptide mapping experiments and immunological criteria demonstrate that these two proteins are not related to each other or to lamin A via postsynthetic modifications or precursor-product relationships. Second, as determined by immunocytochemical techniques, both proteins are located exclusively at the nuclear periphery. Third, both proteins display the biochemical properties characteristic of lamin proteins, i.e. they are resistant to extraction of nuclei with nonionic detergents, nucleases, and high salt. Fourth, both proteins are immunologically related to previously characterized lamin proteins: the major 66-kDa chicken "lamin B" protein shares at least two epitopes with lamin A. However, contrary to what current nomenclature might suggest, this 66-kDa chicken "lamin B" protein is not related to rat liver lamin B, but to a minor component of rat liver pore-complex lamina preparations that had not previously been recognized as a lamin protein. Conversely, the minor 68-kDa component of chicken lamina preparations that had not previously been considered to be a lamin protein is immunologically related to rat liver lamin B. Thus, in addition to demonstrating the existence of quantitatively minor lamin proteins in higher vertebrates, our results caution against assigning structural homologies between lamin proteins from different species on the basis of gel electrophoresis analyses.
核纤层是一种与内核膜紧密相邻的结构，被认为可为核膜完整性和间期染色质组织提供重要的框架。到目前为止，在哺乳动物和鸟类中已鉴定出核纤层的三种主要成分，即核纤层蛋白A、B和C。这些蛋白质在二维凝胶上迁移到特征性位置，核纤层蛋白B比核纤层蛋白A和C的酸性更强。在此，我们表明鸟类和哺乳动物细胞核纤层的组成比以前认为的更为复杂。在二维凝胶上进行分析时，可以很容易地鉴定出主要的66 kDa鸡“核纤层蛋白B”。然而，另一种68 kDa的蛋白质迁移到类似的酸性位置。基于以下证据，这两种蛋白质可被视为核纤层蛋白家族的两个不同成员。首先，肽图谱实验和免疫学标准表明，这两种蛋白质彼此之间以及与核纤层蛋白A之间不存在通过合成后修饰或前体-产物关系的关联。其次，通过免疫细胞化学技术确定，这两种蛋白质都仅位于核周边。第三，这两种蛋白质都表现出核纤层蛋白的生化特性，即它们对用非离子去污剂、核酸酶和高盐提取细胞核具有抗性。第四，这两种蛋白质在免疫学上与先前表征的核纤层蛋白相关：主要的66 kDa鸡“核纤层蛋白B”与核纤层蛋白A至少共享两个表位。然而，与当前的命名法可能暗示的相反，这种66 kDa鸡“核纤层蛋白B”与大鼠肝核纤层蛋白B无关，而是与大鼠肝孔复合体核纤层制剂的一种次要成分相关，该成分以前未被识别为核纤层蛋白。相反，鸡核纤层制剂中以前未被认为是核纤层蛋白的次要68 kDa成分在免疫学上与大鼠肝核纤层蛋白B相关。因此，除了证明高等脊椎动物中存在数量上较少的核纤层蛋白外，我们的结果还提醒人们不要基于凝胶电泳分析来确定不同物种核纤层蛋白之间的结构同源性。
