Shum B P, Azumi K, Zhang S, Kehrer S R, Raison R L, Detrich H W, Parham P
Department of Structural Biology, Standford University, CA 94305, USA.
Proc Natl Acad Sci U S A. 1996 Apr 2;93(7):2779-84. doi: 10.1073/pnas.93.7.2779.
For mammals beta2-microglobulin (beta2m), the light chain of major histocompatibility complex (MHC) class I molecules, is invariant (or highly conserved) and is encoded by a single gene unlinked to the MHC. We find that beta2m of a salmonid fish, the rainbow trout (Oncorhynchus mykiss), does not conform to the mammalian paradigm. Ten of 12 randomly selected beta2m cDNA clones from an individual fish have different nucleotide sequences. A complex restriction fragment length polymorphism pattern is observed with rainbow trout, suggesting multiple beta2m genes in the genome, in excess of the two genes expected from the ancestral salmonid tetraploidy. Additional duplication and diversification of the beta2m genes might have occurred subsequently. Variation in the beta2m cDNA sequences is mainly at sites that do not perturb the structure of the mature beta2m protein, showing that the observed diversity of the trout beta2m genes is not primarily a result of pathogen selection.
对于哺乳动物而言，β2-微球蛋白（β2m）作为主要组织相容性复合体（MHC）I类分子的轻链，具有不变性（或高度保守性），由一个与MHC不连锁的单基因编码。我们发现，鲑科鱼类虹鳟（Oncorhynchus mykiss）的β2m并不符合哺乳动物的模式。从一条虹鳟鱼中随机选取的12个β2m cDNA克隆中有10个具有不同的核苷酸序列。虹鳟呈现出复杂的限制性片段长度多态性模式，这表明其基因组中存在多个β2m基因，数量超过了祖先鲑科鱼类四倍体所预期的两个基因。随后β2m基因可能还发生了额外的复制和多样化。β2m cDNA序列的变异主要发生在不干扰成熟β2m蛋白结构的位点，这表明所观察到的虹鳟β2m基因多样性并非主要由病原体选择导致。
