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a鏈和b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CD8b鏈基因,以及CD8b在Genomic上的圖譜(Restriction Map),並加以定序,結果發現CD8b基因分布在6 kb的範圍,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CD8b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 a and b chains.
In this studies, we report the complete coding sequence of chicken CD8b 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 CD8b 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.

中文摘要: 1
Abstract: 2
縮寫表: 3
緒言:
CD8分子之簡介: 4
CD8分子在T細胞發展過程中所扮演的角色: 4
CD8分子在訊息傳遞上的角色: 6
CD8分子的蛋白質結構: 6
CD8分子的基因結構: 7
從演化觀點看CD8分子: 9
本篇論文所要處理的問題: 9
實驗材料與方法: 10
實驗結果: 16
實驗討論: 28
參考文獻: 38
附錄一:雞的CD8a鏈之cDNA序列 42
附錄二:雞的CD8b鏈之cDNA序列 43
附錄三:雞的CD8a鏈基因和氨基酸之序列 45
附錄四:Genomic organization of CD8a gene 50
附錄五:The amino acid sequence comparison 51
of CD8a of chicken ,mouse and human.

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