中文摘要：

主要组织相容性I（MHC Ⅰ）类抗原分子重链基因是目前所有蛋白分子中多态性最高的分子。MHC Ⅰ分子重链有5个功能结构域,包括α1、α2、α3跨膜和胞浆区,其中α1和α2又是I类分子中多态性最高的区域。总的来讲,α1和α2结构域与等位基群或等位基因族系相关,而α3和跨膜及胞浆域与MHC Ⅰ类分子基因座相关。人们对MHC Ⅰ认识和知识主要来自人和鼠MHC Ⅰ研究,人和鼠MHC Ⅰ不存在基因座重叠现象,但最近研究发现灵长类MHC Ⅰ基因座存在重叠现象。生物学方法克服血清学方法不能定义或确定I类分子的基因座的缺点。本项目选择2只来自不同品系的绵羊,通过对它们的MHC Ⅰ类分子α1和α2 cD NA的克隆、测序和分析,研究绵羊MHC Ⅰ类分子多态性,并探索该基因在绵羊中是否存在基因座重叠现象。对来自2只绵羊20个α1和α2区域cD NA序列分析,2只绵羊9个或11个α1和α2 cD NA分子表明它们至少有5或6个MHC Ⅰ类分子等位基因。比较目前所有绵羊MHC Ⅰ类分子α1和α2 cD NA序列,结合分析α3跨膜区和胞浆区cD NA序列,参照目前单位片分析确定的绵羊MHC Ⅰ类分子基因座分布,我们发现绵羊MHCI分子基因存在基因重叠现象。

英文摘要：

The heavy chain encoded by the class I major histocompatibility complex（MHC） is among the most polymorphic molecule characterized. It consists of α1, α2, α3, transmembrane and cytoplasmic domains, and of these five domains the α1 and α2 domains are the most polymorphic regions. In general, α1- α2 domains reflect alleles and allele families, and α3- cytoplasmic domains delineate loci and contact motifs specific to loci. There are difficulties in using serological techniques to define MHC class I, and often now, molecular techniques are used. To investigate the polymorphisms and number of transcribed ovine MHC class I genes in individual animals, cD NA fragments of MHC class I α1- α2 domains from two sheep breeds were amplified by reverse transcriptase polymerase chain reaction（RT- PCR）,PCR products were cloned, sequenced and analysed. Sequencing results showed in total 20 sequences of ovine MHC class I α1- α2 domain cD NAs obtained from these sheep. The homology of these cD NA sequences ranged between 53%and 99%, indicating how polymorphic the clones were. Eleven sequences obtained from a single sheep gave evidence that at least six loci encoding ovine class I heavy chain genes were transcribed. Comparative phylogenetic analyses of cD NA sequence data of α1- α2 and α3- cytoplasmic domains reflected the existence of ovine MHC class I locus duplication causing the complexity of allelic family and locus assignment.