Hu T, Gerace L
Department of Cell Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA.
Gene. 1998 Oct 23;221(2):245-53. doi: 10.1016/s0378-1119(98)00467-3.
The p62 complex is an assembly of four O-linked glycoproteins (p62, p58, p54, and p45) localized in the central region of the nuclear pore complex. It has been suggested to provide a substrate binding site near the central gated channel of the pore during nuclear protein import. The sequences of p62, p58, and p54 from rat have been reported previously. We have now carried out cDNA cloning of rat p45. The authenticity of the p45 clone was confirmed by two-dimensional gel analysis of the in vitro translated product of this clone. Sequence comparison showed that p45 is mostly identical to the amino terminal four-fifths of p58. p45 contains an N-terminal FG (Phe-Gly) repeat region, a middle coiled-coil region, and a truncated C-terminal FG repeat region (compared to p58). The sequence data and genomic Southern hybridization results strongly support the possibility that p45 and p58 are generated by mRNA alternative splicing. The sequences of three other p58-related cDNA clones indicate that the p58/p45 gene transcript gives rise to additional alternatively spliced mRNAs in mammalian cells. Interestingly, the expression level of p45 relative to p58 varies in different cultured cell lines, indicating that the p62 complex is heterogeneous with respect to these two subunits.
p62复合体是由四种O-连接糖蛋白（p62、p58、p54和p45）组成的装配体，定位于核孔复合体的中央区域。有人提出，在核蛋白输入过程中，它在核孔的中央门控通道附近提供一个底物结合位点。大鼠p62、p58和p54的序列此前已有报道。我们现在对大鼠p45进行了cDNA克隆。通过对该克隆的体外翻译产物进行二维凝胶分析，证实了p45克隆的真实性。序列比较表明，p45与p58氨基末端的五分之四基本相同。p45包含一个N端FG（苯丙氨酸-甘氨酸）重复区域、一个中间的卷曲螺旋区域和一个截短的C端FG重复区域（与p58相比）。序列数据和基因组Southern杂交结果有力地支持了p45和p58是由mRNA可变剪接产生的可能性。另外三个与p58相关的cDNA克隆的序列表明，p58/p45基因转录本在哺乳动物细胞中产生了其他可变剪接的mRNA。有趣的是，p45相对于p58的表达水平在不同的培养细胞系中有所不同，这表明p62复合体在这两个亚基方面是异质的。
