Widera G, Flavell R A
Proc Natl Acad Sci U S A. 1985 Aug;82(16):5500-4. doi: 10.1073/pnas.82.16.5500.
In the C57BL/10 mouse, 140 kilobases (kb) of the I region (I-Ab, I-Eb) were isolated as recombinant cosmids. The class II genes A beta 2, A beta 1, A alpha,E beta 1, E beta 2, and E alpha are located from centromere to telomere in a region of approximately equal to 110 kb, which shows that the I region in the b haplotype has a similar overall organization to those described for the d, k, and wr7 haplotypes. In addition to these genes, we have also isolated a class II gene, psi A beta 3, which is physically linked to the class I H-2K region, 75 kb telomeric to the H-2Kb gene. This orients the H-2K region on the genetic map with the H-2Kb gene being located toward the I region. The sequence of the beta 2 domain of psi A beta 3 is similar to the immunoglobulin-like domain of other class II genes. Interestingly, it shows 83% nucleotide homology to the human SB beta gene, the same homology that was seen previously between the immunoglobulin-like exons of A beta 1 and DC beta and between E beta 1 and DR beta, respectively. It is likely, therefore, that psi A beta 3 represents a member of a third SB-like class II gene family present in addition to I-A and I-E genes and that the divergence of the SB family predates the speciation of rodents and primates. Comparison of the DNA sequence of the exon encoding the beta 2 domain of psi A beta 3 in the b or k haplotypes with functional class II genes shows that a deletion of eight nucleotides has occurred, such that the psi A beta 3 sequence cannot be translated into a functional class II protein. This suggests that psi A beta 3 is a pseudogene.
在C57BL/10小鼠中，I区（I-Ab、I-Eb）的140千碱基（kb）作为重组黏粒被分离出来。II类基因Aβ2、Aβ1、Aα、Eβ1、Eβ2和Eα从着丝粒到端粒位于大约110 kb的区域内，这表明b单倍型中的I区具有与d、k和wr7单倍型中所描述的相似的整体组织。除了这些基因，我们还分离出了一个II类基因psi Aβ3，它与I类H-2K区物理连锁，位于H-2Kb基因端粒方向75 kb处。这在遗传图谱上确定了H-2K区的方向，其中H-2Kb基因朝向I区。psi Aβ3的β2结构域序列与其他II类基因的免疫球蛋白样结构域相似。有趣的是，它与人类SBβ基因有83%的核苷酸同源性，这与之前在Aβ1和DCβ以及Eβ1和DRβ的免疫球蛋白样外显子之间分别观察到的同源性相同。因此很可能，psi Aβ3代表了除I-A和I-E基因之外存在的第三个类似SB的II类基因家族的成员，并且SB家族的分化早于啮齿动物和灵长类动物的物种形成。将b或k单倍型中编码psi Aβ3的β2结构域的外显子的DNA序列与功能性II类基因进行比较表明，发生了八个核苷酸的缺失，使得psi Aβ3序列无法翻译成功能性II类蛋白。这表明psi Aβ3是一个假基因。
