Rizwana R, Hahn P J
Department of Radiation Oncology, State University of New York Health Science Center, Syracuse 13210, USA.
Genomics. 1998 Jul 15;51(2):207-15. doi: 10.1006/geno.1998.5396.
Double-minute chromosomes (DMs) amplify oncogenes in human tumors. The organization of genomic DNA in four independently isolated DMs amplifying the DHFR (dihydrofolate reductase) gene has been compared by mapping locations of CpG islands. When cleaved with methylation-sensitive rare-cutting restriction endonucleases, three hypomethylated GC-rich DNA sequences were frequently found in specific regions in these DMs. One such zone was in the CpG island containing the divergently transcribed promoter separating the DHFR and the Rep-3 genes. The other two sites were approximately 500 kb upstream and 300 kb downstream of the DHFR gene. An approximately 800-kb amplified core genomic region containing the DHFR gene using DM-specific probes has been identified in this study. All the DMs consisted of the core amplified region combined with additional DNA fragments. These additional fragments are different for each DM. Therefore, while the DNAs in each of the DMs are different, they have common hypomethylated regions in similar locations. These results suggest a role for the location of hypomethylated GC-rich sites such as the CpG islands in genesis of DMs.
双微体染色体（DMs）在人类肿瘤中会扩增癌基因。通过绘制CpG岛的位置，比较了四个独立分离的扩增二氢叶酸还原酶（DHFR）基因的DMs中基因组DNA的组织情况。用甲基化敏感的稀有切割限制性内切酶切割时，在这些DMs的特定区域经常发现三个低甲基化的富含GC的DNA序列。其中一个区域位于包含将DHFR和Rep-3基因分开的反向转录启动子的CpG岛内。另外两个位点分别位于DHFR基因上游约500 kb和下游约300 kb处。在本研究中，使用DM特异性探针鉴定了一个包含DHFR基因的约800 kb的扩增核心基因组区域。所有的DMs都由核心扩增区域与其他DNA片段组成。这些额外的片段在每个DM中都不同。因此，虽然每个DM中的DNA不同，但它们在相似位置有共同的低甲基化区域。这些结果表明，诸如CpG岛等低甲基化富含GC的位点的位置在DMs的形成中起作用。
