The isolation and characterization of chicken CD8 chain gene

• Main Authors: Liao, Hong Jun, 廖泓鈞
• Other Authors: Guo, Qie Lan
• Format: Others
• Language: zh-TW
• Published: 1995
• Online Access: http://ndltd.ncl.edu.tw/handle/45007824283194832556

碩士 === 國立臺灣大學 === 生化科學研究所 === 83 === 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 lymphocyte with their targets, and as a signal transduction unit. CD8 exists as a disulfide-linked heterodimer of the alpha- and beta- chains. Here we report the complete coding sequence of chicken CD8 alpha gene, and its genomic organization. This gene spans approximately 6kb and is organized into six exons which encode separate functional domains of the protein. Exon I encodes the 5'untranslated region and leader sequence, exon II the Ig V-like region, exon III the hindge region, exon IV the transmembrane domain, and exon V, VI the cytoplasmic tail. Comparison of the CD8 alpha gene of human, mouse, and chicken has revealed a high homology in structure, especially the transmembrane domain and the cytoplasmic domain(70% homology). CD8 molecules are a member of immunoglobulin gene superfamily. The V-like region of CD8 alpha has homology to Ig V and TCR V region. Using V-like region DNA segments of CD8 alpha as probes, we found there are many homologous DNA fragments shown by genomic blot hybridization. After sequencing two of them, named BamHI1.2k and BamHI0.9k, which locate upstream of CD8 alpha, we found that they are highly homologous to Ig V kappa light chain. The amino acid required for the formation of the immuonglobulin fold, such as the two cysteines involved in intrachain disulfide bond formation and the invariant tryptophan, are located in the expected position. There is no report about Ig kappa light chain of chicken so far. But it is known Ig kappa light chain are located on the same chromosome in both human and mouse. It is possible BamHI1.2k and BamHI0.9k are the ancestor of Ig V kappa light chain.