Nielsen L, Schmidt E R, Edström J E
Department of Genetics, Lund, Sweden.
J Mol Biol. 1990 Dec 5;216(3):577-84. doi: 10.1016/0022-2836(90)90385-Y.
Repeat units, widespread in eukaryotic genomes, are often partially or entirely built up of subrepeats. Homogenization between whole repeat units arranged in tandem usually can best be understood as a result of unequal crossing over. Such a mechanism is less plausible for maintaining similarities between subrepeats within a repeat unit when present in a regular array. In Chironomus telomeres, large blocks of tandemly repeated approximately 350 base-pair units contain two or three pairs of subrepeats with high mutual identities, embedded in linker DNA, non-repetitive within the repeat unit. Measurements of evolutionary base changes in two closely related species, Chironomus tentans and Chironomus pallidivittatus, permit us to conclude that the subrepeat arrangement is best explained as a consequence of regional sequence conservation after an earlier duplication of an ancestral half-unit.
重复单元在真核生物基因组中广泛存在，通常部分或全部由亚重复序列构成。串联排列的整个重复单元之间的同质化通常最好理解为不等交换的结果。当以规则阵列形式存在时，这种机制对于维持重复单元内亚重复序列之间的相似性不太合理。在摇蚊的端粒中，大量串联重复的约350个碱基对单元的大片段包含两对或三对具有高度相互同源性的亚重复序列，嵌入在连接DNA中，在重复单元内是非重复的。对两个密切相关的物种——细摇蚊和苍白摇蚊——进化碱基变化的测量使我们能够得出结论，亚重复序列的排列最好解释为祖先半单元早期复制后区域序列保守的结果。
