雞的CD8β鏈基因之分離與鑑定

Abstract

CD8分子是一種醣蛋白，由T細胞所表現至細胞膜上。CD8分子主要辨認MHC class I 分子，在CTL(Cytotoxic T cell) 細胞的活化和執行刺殺任務時，扮演加強和目標物結合的親和力，和訊息傳遞的角色.在結構上主要是由α鏈和β鏈以heterodimer 的型式出現，兩條鏈間以雙硫鍵鍵結。 本篇論文，主要在確定雞的CD8β鏈基因，以及CD8β在Genomic 上的圖譜(Restriction Map)，並加以定序，結果發現CD8β基因分佈在6kb的範園，由五個Exons 組成，分別是:Exon I是5'Untranslated region 和Leader peptide ; Exon II 是Ig VJ-like region ; Exon III 是Membrane Proximal region ; Exon IV 是Transmembrane domain ; Exon V 是Cytplasmic domain 和3'untranslated region。 我們並以雞的CD8β基因和人跟老鼠作比較，發現三者在結構上都很相似，尤其是Transmembrane domain 和Cytoplasmic domain 相似性更高。有趣的是，我們也確認了一段non-coding region，它的序列和PKCI'基因之3'端之Flanking region 有很高的相似性。而此段non-coding region 的重要性可能是調控此region附近之基因的genome structure ，copy number 和expression 的功能。

The CD8 glycoprotein is expressed on the surface of T lymphocytes. CD8 is thought to bind MHC class I molecules and to function both as an adhesion molecule, stabilizing the interaction of T lymphocytes with their targets, and as a signal transduction unit. CD8 exists as a disulfide-linked heterodimer of the α and β chains. In this studies, we report the complete coding sequence of chicken CD8 gene, and its genomic organization. This gene spans approximately 6 kb and is organized into five exons which encode separate functional domains of the protein. Exon I encodes the 5' untranslated region and leader peptide, Exon II encodes the Ig VJ-like domain, Exon III encodes the membrane proximal region, Exon IV encodes transmembrane domain, Exon V encodes Cytoplasmic domain and 3' untranslated region, indicating a high degree of conservation in the genomic organization among chicken, mouse and human. Comparison of the sequence of the CD8β gene of human, mouse, and chicken has revealed a high degree of homology , especially at the transmembrane domain and the cytoplasmic domain. Interestingly, we have also identified a non-coding region with sequences highly homologous to the 3' flanking region of PKCI' gene. The potential significance with regard to the control on the genome structure, copy number and expression of the gene(s) adjacent to this region is discussed.