Plass C, Hellwig T, Traut W, Winking H
Institut für Biologie, Medizinische Universität zu Lübeck, FRG.
Mamm Genome. 1992;3(4):197-201. doi: 10.1007/BF00355719.
A long-range repeat family of more than 50 kb repeat size is clustered in Chromosomes (Chr) 1 of Mus musculus and M. spretus. In M. musculus this long-range repeat family shows considerable variation of copy-number frequency and contains coding regions for at least two genes. In an intron of a gene, which is part of the repeat, a B2 small interspersed repetitive element (SINE) is inserted at identical positions. The B2 element is present in all copies of the long-range repeat family; it was presumably a component of the ancestral single-copy precursor sequence that gave rise by amplification to the repeat family. Copies of the long-range repeat family vary with respect to the number of TAAA tandem repeats in the A-rich 3' end region of the B2 element. As inferred from polymerase chain reaction (PCR) data, presence and frequency of repeat number variants in the (TAAA)n block are strain and species specific. The B2 element and its flanking regions were sequenced from two copies of the long-range repeat family. Sequence divergence between the two copies (only non-CG base substitutions and deletions/insertions) was determined to be 2.6%. Based on the drift rate in human Alu elements and a correction for the higher drift rates in rodents, an estimate for the divergence time of 1.7 million years was calculated. Since the long-range repeat family is present in M. musculus and M. spretus, it must have evolved by amplification before the separation of the two species about 1-4 million years ago.
一个重复大小超过50 kb的长程重复家族聚集在小家鼠和西班牙小鼠的1号染色体上。在小家鼠中，这个长程重复家族的拷贝数频率有相当大的变化，并且包含至少两个基因的编码区。在作为重复序列一部分的一个基因的内含子中，一个B2小散在重复元件（SINE）插入在相同位置。B2元件存在于长程重复家族的所有拷贝中；它可能是祖先单拷贝前体序列的一个组成部分，该前体序列通过扩增产生了这个重复家族。长程重复家族的拷贝在B2元件富含A的3'端区域的TAAA串联重复次数方面有所不同。根据聚合酶链反应（PCR）数据推断，（TAAA）n块中重复数变体的存在和频率具有品系和物种特异性。从长程重复家族的两个拷贝中对B2元件及其侧翼区域进行了测序。确定两个拷贝之间的序列差异（仅非CG碱基替换和缺失/插入）为2.6%。根据人类Alu元件的漂移率以及对啮齿动物较高漂移率的校正，计算出分歧时间估计为170万年。由于长程重复家族存在于小家鼠和西班牙小鼠中，它一定是在大约100万至400万年前这两个物种分离之前通过扩增进化而来的。
