Rozmahel R, Heng H H, Duncan A M, Shi X M, Rommens J M, Tsui L C
Department of Molecular and Medical Genetics, The University of Toronto, Toronto, Ontario, M5S 1A7.
Genomics. 1997 Nov 1;45(3):554-61. doi: 10.1006/geno.1997.4968.
Cloning and characterization of the cystic fibrosis transmembrane conductance regulator (CFTR) gene led to the identification and isolation of cDNA and genomic sequences that cross-hybridized to the first nucleotide binding fold of CFTR. DNA sequence analysis of these clones showed that the cross-hybridizing sequences corresponded to CFTR exon 9 and its flanking introns, juxtapositioned with two segments of LINE1 sequences. The CFTR sequence appeared to have been transcribed from the opposite direction of the gene, reversely transcribed, and co-integrated with the L1 sequences into a chromosome location distinct from that of the CFTR locus. Based on hybridization intensity and complexity of the restriction fragments, it was estimated that there were at least 10 copies of the "amplified" CFTR exon 9 sequences in the human genome. Furthermore, when DNA segments adjacent to the insertion site were used in genomic DNA blot hybridization analysis, multiple copies were also detected. The overall similarity between these CFTR exon 9-related sequences suggested that they were derived from a single retrotransposition event and subsequent sequence amplification. The amplification unit appeared to be greater than 30 kb. Physical mapping studies including in situ hybridization to human metaphase chromosomes showed that multiple copies of these amplified sequences (with and without the CFTR exon 9 insertion) were dispersed throughout the genome. These findings provide insight into the structure and evolution of the human genome.
囊性纤维化跨膜传导调节因子（CFTR）基因的克隆与特性分析，使得与CFTR第一个核苷酸结合结构域发生交叉杂交的cDNA和基因组序列得以鉴定和分离。对这些克隆进行的DNA序列分析表明，交叉杂交序列对应于CFTR外显子9及其侧翼内含子，并与两段LINE1序列并列。CFTR序列似乎是从该基因的相反方向转录而来，经过逆转录，并与L1序列共同整合到一个与CFTR基因座不同的染色体位置。根据限制片段的杂交强度和复杂性估计，人类基因组中至少有10个拷贝的“扩增”CFTR外显子9序列。此外，当在基因组DNA印迹杂交分析中使用插入位点附近的DNA片段时，也检测到了多个拷贝。这些与CFTR外显子9相关的序列之间的总体相似性表明，它们源自单个逆转座事件及随后的序列扩增。扩增单元似乎大于30 kb。包括对人类中期染色体进行原位杂交在内的物理图谱研究表明，这些扩增序列的多个拷贝（有和没有CFTR外显子9插入）分散在整个基因组中。这些发现为人类基因组的结构和进化提供了见解。
