Ivanov S V, Modi W S
Biological Carcinogenesis and Development Program, SAIC Frederick, National Cancer Institute-Frederick Cancer Research and Development Center, MD 21702-1201, USA.
Cytogenet Cell Genet. 1996;75(1):49-56. doi: 10.1159/000134456.
The sex chromosomes of Microtus chrotorrhinus are unusually large compared to those of other mammals, comprising about 20% of the karyotype and containing substantial amounts of constitutive heterochromatin. Previous studies have described two highly repeated DNA families (MSAT-160 and MSAT-2570) that localize to this heterochromatin (Modi, 1992, 1993c). The present report describes a third satellite DNA family (termed MSAT-21) in M. chrotorrhinus that is also located in the sex heterochromatin. This repeat consists of diverged copies (average similarity = 75%) of a tandemly repeated 21-mer. Southern blotting of MSAT-21 revealed that although some higher order (5-20 kb) repeats do exist, none has spread throughout an appreciable portion of the genome. Pulsed field gel experiments indicated that most of the larger arrays (50-700 kb) of all three satellite families are distributed across numerous size classes, suggesting that the three repeats are interspersed with one another in this heterochromatin. Analysis of a boundary between MSAT-21 and MSAT-160 showed that the junction monomers of each satellite are intact and that a pentanucleotide has apparently been transferred from MSAT-21 to MSAT-160 via recombination. Sequence comparisons of MSAT-160 with another rodent satellite and with the U3 region of the Rous sarcoma virus (RSV) long terminal repeat identified inverted repeats and similarities with viral enhancer domains in the rodent sequences. Additionally, the MSAT-21 consensus was found to be similar to the R region of RSV, suggesting a retroviral ancestor for these rodent repeated DNA families.
与其他哺乳动物相比，棕色田鼠的性染色体异常大，约占核型的20%，并含有大量的组成型异染色质。先前的研究描述了两个高度重复的DNA家族（MSAT - 160和MSAT - 2570），它们定位于这种异染色质（莫迪，1992年，1993c）。本报告描述了棕色田鼠中的第三个卫星DNA家族（称为MSAT - 21），它也位于性异染色质中。这个重复序列由一个串联重复的21聚体的分化拷贝组成（平均相似度 = 75%）。MSAT - 21的Southern印迹分析表明，虽然确实存在一些高阶（5 - 20 kb）重复序列，但没有一个在基因组的相当一部分中扩散。脉冲场凝胶实验表明，所有三个卫星家族的大多数较大阵列（50 - 700 kb）分布在多个大小类别中，这表明这三个重复序列在这种异染色质中相互穿插。对MSAT - 21和MSAT - 160之间边界的分析表明，每个卫星的连接单体是完整的，并且一个五核苷酸显然通过重组从MSAT - 21转移到了MSAT - 160。MSAT - 160与另一种啮齿动物卫星以及劳斯肉瘤病毒（RSV）长末端重复序列的U3区域的序列比较确定了反向重复序列以及与啮齿动物序列中病毒增强子结构域的相似性。此外，发现MSAT - 21的共有序列与RSV的R区域相似，这表明这些啮齿动物重复DNA家族有逆转录病毒祖先。
