Hsu T C, Shore S K, Seshsmma T, Bagasra O, Walsh P N
Department of Biochemistry, Temple University School of Medicine, Philadelphia, Pennsylvania 19140, USA.
J Biol Chem. 1998 May 29;273(22):13787-93. doi: 10.1074/jbc.273.22.13787.
Platelet factor XI is associated with the platelet plasma membrane and has an apparent Mr (220,000 nonreduced, 55,000 reduced) different from that of plasma factor XI. However, the site of synthesis and the nature of platelet factor XI are not known. Using reverse transcriptase polymerase chain reaction, 12 out of 13 exons (all except exon V) coding for mature plasma factor XI were amplified from human platelet mRNA. The sequence of each of these exons was identical to that of plasma factor XI. In situ amplification and hybridization of factor XI mRNA was positive for exon III and negative for exon V in platelets and negative for both exons in other blood cells. By Northern hybridization, a factor XI mRNA transcript of approximately 1.9 kilobases was detected in megakaryocytic cells, and one of approximately 2.1 kilobases was detected in liver cells. Factor XI cDNA was cloned from a megakaryocyte library and sequenced. Exon V was absent, and the splicing of exon IV to exon VI maintained the open reading frame without alteration of the amino acid sequence except for the deletion of amino acids Ala91-Arg144 within the amino-terminal portion of the Apple 2 domain. Thus, platelet factor XI is an alternative splicing product of the factor XI gene, localized to platelets and megakaryocytes but absent from other blood cells.
血小板因子XI与血小板质膜相关，其表观分子量（非还原状态下为220,000，还原状态下为55,000）与血浆因子XI不同。然而，血小板因子XI的合成位点和性质尚不清楚。利用逆转录聚合酶链反应，从人血小板mRNA中扩增出了编码成熟血浆因子XI的13个外显子中的12个（除了外显子V）。这些外显子中的每一个的序列都与血浆因子XI的序列相同。血小板中外显子III的因子XI mRNA原位扩增和杂交呈阳性，外显子V呈阴性，其他血细胞中两个外显子均呈阴性。通过Northern杂交，在巨核细胞中检测到一条约1.9千碱基的因子XI mRNA转录本，在肝细胞中检测到一条约2.1千碱基的转录本。从巨核细胞文库中克隆并测序了因子XI cDNA。外显子V缺失，外显子IV与外显子VI的剪接维持了开放阅读框，除了苹果2结构域氨基末端部分的氨基酸Ala91-Arg144缺失外，氨基酸序列未改变。因此，血小板因子XI是因子XI基因的一种可变剪接产物，定位于血小板和巨核细胞，但在其他血细胞中不存在。
