Newman S, Kitamura K, Campagnoni A T
Proc Natl Acad Sci U S A. 1987 Feb;84(3):886-90. doi: 10.1073/pnas.84.3.886.
The primary sequences of four molecular mass variants (14, 17, 18.5, and 21.5 kDa) of the mouse myelin basic protein (MBP) have recently been determined through analysis of cDNA clones of their mRNAs. The mRNAs coding for the four MBP variants are thought to arise by differential splicing of two exons (exons 2 and 6) from a single gene. In contrast, exons 2 and 5 may be spliced out in the posttranscriptional processing of the human MBP gene. To investigate the possibility that a third exon (exon 5) may also be differentially spliced out in the processing of the mouse MBP gene transcript, a mouse cDNA library was screened to search for cDNAs missing exon 5. A MBP cDNA was isolated whose coding region specified a fifth mouse MBP variant with a molecular mass of approximately equal to 17 kDa. The mass of this variant (17,257 Da) is so close to that of the other 17-kDa mouse MBP (17,224 Da) that the two would be indistinguishable on NaDodSO4/polyacrylamide gels. Analysis of the sequence of the cDNA clone indicates that excision of exons 2 and 5 of the mouse MBP gene would produce the mRNA encoding this newly described 17-kDa MBP, whereas excision of exon 6 would produce the mRNA for the other 17-kDa MBP variant. Thus, the "17-kDa" mouse MBP consists of at least two molecular forms with very similar molecular masses but markedly different primary sequences. Of five full-length or near full-length cDNAs representing 17-kDa MBPs, one was missing exons 2 and 5 and four were missing exon 6.
最近，通过对小鼠髓鞘碱性蛋白（MBP）四种分子量变体（14、17、18.5和21.5 kDa）的mRNA的cDNA克隆进行分析，确定了它们的一级序列。编码这四种MBP变体的mRNA被认为是由单个基因的两个外显子（外显子2和6）的差异剪接产生的。相比之下，外显子2和5可能在人类MBP基因的转录后加工过程中被剪接掉。为了研究在小鼠MBP基因转录本的加工过程中第三个外显子（外显子5）也可能被差异剪接掉的可能性，筛选了一个小鼠cDNA文库以寻找缺失外显子5的cDNA。分离出一个MBP cDNA，其编码区确定了第五种小鼠MBP变体，分子量约为17 kDa。这种变体的质量（17,257 Da）与另一种17-kDa小鼠MBP（17,224 Da）非常接近，以至于在十二烷基硫酸钠/聚丙烯酰胺凝胶上两者无法区分。对该cDNA克隆序列的分析表明，切除小鼠MBP基因的外显子2和5会产生编码这种新描述的17-kDa MBP的mRNA，而切除外显子6会产生另一种17-kDa MBP变体的mRNA。因此，“17-kDa”小鼠MBP至少由两种分子量非常相似但一级序列明显不同的分子形式组成。在代表17-kDa MBP的五个全长或接近全长的cDNA中，一个缺失外显子2和5，四个缺失外显子6。
