Cullen M, Noble J, Erlich H, Thorpe K, Beck S, Klitz W, Trowsdale J, Carrington M
Intramural Research Support Program, SAIC Frederick, National Cancer Institute--Frederick Cancer Research and Development Center, MD 21702, USA.
Am J Hum Genet. 1997 Feb;60(2):397-407.
Studies of linkage disequilibrium across the HLA class II region have been useful in predicting where recombination is most likely to occur. The strong associations between genes within the 85-kb region from DQB1 to DRB1 are consistent with low frequency of recombination in this segment of DNA. Conversely, a lack of association between alleles of TAP1 and TAP2 (approximately 15 kb) has been observed, suggesting that recombination occurs here with relatively high frequency. Much of the HLA class II region has now been sequenced, providing the tools to undertake detailed analysis of recombination. Twenty-seven families containing one or two recombinant chromosomes within the 500-kb interval between the DPB1 and DRB1 genes were used to determine patterns of recombination across this region. SSCP analysis and microsatellite typing yielded identification of 127 novel polymorphic markers distributed throughout the class II region, allowing refinement of the site of crossover in 30 class II recombinant chromosomes. The three regions where recombination was observed most frequently are as follows: the 45-kb interval between HLA-DNA and RING3 (11 cases), the 50-kb interval between DQB3 and DQB1 (6 cases), and an 8.8-kb segment of the TAP2 gene (3 cases). Six of the 10 remaining recombinants await further characterization, pending identification of additional informative markers, while four recombinants were localized to other intervals (outliers). Analysis of association between markers flanking HLA-DNA to RING3 (45 kb), as well as TAP1 to TAP2 (15 kb), by use of independent CEPH haplotypes indicated little or no linkage disequilibrium, supporting the familial recombination data. A notable sequence motif located within a region associated with increased rates of recombination consisted of a (TGGA)12 tandem repeat within the TAP2 gene.
对HLA II类区域连锁不平衡的研究有助于预测重组最可能发生的位置。从DQB1到DRB1的85 kb区域内各基因之间的强关联，与该DNA片段中低频率的重组情况相符。相反，已观察到TAP1和TAP2等位基因（约15 kb）之间缺乏关联，这表明该区域重组频率相对较高。现在，HLA II类区域的大部分已完成测序，为进行重组的详细分析提供了工具。利用27个在DPB1和DRB1基因之间500 kb区间内含有一到两条重组染色体的家系，来确定该区域的重组模式。单链构象多态性分析（SSCP）和微卫星分型鉴定出了127个分布于整个II类区域的新型多态性标记，从而能够在30条II类重组染色体中更精确地确定交叉位点。观察到重组最频繁的三个区域如下：HLA-DNA与RING3之间的45 kb区间（11例）、DQB3与DQB1之间的50 kb区间（6例）以及TAP2基因的8.8 kb片段（3例）。其余10条重组体中有6条有待进一步鉴定，有待发现更多信息性标记，而另外4条重组体定位到了其他区间（异常值）。利用独立的CEPH单倍型对HLA-DNA至RING3（45 kb）以及TAP1至TAP2（15 kb）两侧的标记进行关联分析，结果显示连锁不平衡很少或不存在，这支持了家族性重组数据。位于与重组率增加相关区域内的一个显著序列基序是TAP2基因内的（TGGA）12串联重复序列。
