Origin of human chromosome 2: an ancestral telomere-telomere fusion.

We have identified two allelic genomic cosmids from human chromosome 2, c8.1 and c29B, each containing two inverted arrays of the vertebrate telomeric repeat in a head-to-head arrangement, 5'(TTAGGG)n-(CCCTAA)m3'. Sequences flanking this telomeric repeat are characteristic of present-day human pretelomeres. BAL-31 nuclease experiments with yeast artificial chromosome clones of human telomeres and fluorescence in situ hybridization reveal that sequences flanking these inverted repeats hybridize both to band 2q13 and to different, but overlapping, subsets of human chromosome ends. We conclude that the locus cloned in cosmids c8.1 and c29B is the relic of an ancient telomere-telomere fusion and marks the point at which two ancestral ape chromosomes fused to give rise to human chromosome 2. IMAGES:

我们已从人类2号染色体中鉴定出两种等位基因组黏粒（cosmid）c8.1与c29B，二者均以头对头的排列方式，各包含两套脊椎动物端粒重复序列的反向阵列，其重复序列为5'(TTAGGG)n-(CCCTAA)m3'。该端粒重复序列的侧翼序列，具备当代人类前端粒序列的典型特征。通过对人类端粒的酵母人工染色体克隆进行BAL-31核酸酶实验，并结合荧光原位杂交（fluorescence in situ hybridization, FISH）分析，结果显示：这些反向重复序列的侧翼序列既能与2q13区带杂交，也可与人类染色体末端不同但存在重叠的子集发生杂交。我们由此推断，黏粒c8.1与c29B所克隆的基因座，是一次古老端粒-端粒融合事件的遗迹，同时也标记了两条类人猿祖先染色体融合形成人类2号染色体的位点。图像：