CRISPR-Cas是基于核酸的原核免疫系统。CRISPR阵列从外源DNA积累间隔区并提供对含有相同或相似序列的可移动遗传元件的抗性。因此，一组存在于给定细菌中的间隔区可以被视为其祖先与遗传入侵者相遇的记录。这些记录应该是特定于不同的血统和随时间的变化，因为早期获得的间隔物会过时并丢失。这里,我们从已灭绝的厚皮动物中研究了大肠杆菌的I-E型CRISPR间隔区。我们发现，从42.000岁的猛犸象的肠道中回收的许多间隔物与当今的大肠杆菌的间隔物相匹配。目前的CRISPR阵列可以从古序列中重建，表明间隔物的顺序也得到了保留。结果表明,在这段时间内,大肠杆菌CRISPR阵列不经受通过自适应采集的密集变化。
CRISPR-Cas are nucleic acid-based prokaryotic immune systems. CRISPR arrays accumulate spacers from foreign DNA and provide resistance to mobile genetic elements containing identical or similar sequences. Thus, the set of spacers present in a given bacterium can be regarded as a record of encounters of its ancestors with genetic invaders. Such records should be specific for different lineages and change with time, as earlier acquired spacers get obsolete and are lost. Here, we studied type I-E CRISPR spacers of Escherichia coli from extinct pachyderm. We find that many spacers recovered from intestines of a 42 000-year-old mammoth match spacers of present-day E. coli. Present-day CRISPR arrays can be reconstructed from palaeo sequences, indicating that the order of spacers has also been preserved. The results suggest that E. coli CRISPR arrays were not subject to intensive change through adaptive acquisition during this time.
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