Clustered regularly interspaced short palindrome repeats (CRISPRs) have spacers of extrachromosomal origin
Clustered regularly interspaced short palindrome repeats (CRISPRs) have spacers of extrachromosomal origin
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DOI：
10.1099/mic.0.28048-0
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发表时间：
2005-08-01
期刊：
影响因子：
2.8
通讯作者：
Ehrlich, SD
中科院分区：
文献类型：
--
作者：
Bolotin, A;Ouinquis, B;Ehrlich, SD
许多原核生物基因组都含有被称为簇状规则间隔短回文重复序列（crispr）的结构，由25-50 bp的重复序列组成，由长度相似的独特序列间隔器分隔。CRISPR结构位于cas1到cas4四个基因附近。计算机分析揭示了在许多细菌物种中与CRISPR结构相关的另外三个基因簇，本文将其命名为cas1B、cas5和cas6，并且还揭示了一定数量的与现存基因同源的间隔序列，这些间隔序列最常来源于噬菌体，但也来源于其他染色体外元件。对24株嗜热链球菌和前庭链球菌的CRISPR结构进行序列分析，证实了间隔序列与染色体外元件的同源性。嗜热葡萄球菌菌株的噬菌体敏感性似乎与菌株携带的CRISPR位点的间隔片段数量有关。作者认为，间隔元件是染色体外元件过去入侵的痕迹，并假设它们通过编码反义RNA提供细胞对噬菌体感染的免疫，以及更普遍的外源DNA表达。CRISPR结构中存在基因片段，两种簇型的cas基因中存在核酸酶基序，这表明CRISPR的形成涉及DNA降解步骤。
Numerous prokaryote genomes contain structures known as clustered regularly interspaced short palindromic repeats (CRISPRs), composed of 25-50 bp repeats separated by unique sequence spacers of similar length. CRISPR structures are found in the vicinity of four genes named cas1 to cas4. In silico analysis revealed another cluster of three genes associated with CRISPR structures in many bacterial species, named here as cas1B, cas5 and cas6, and also revealed a certain number of spacers that have homology with extant genes, most frequently derived from phages, but also derived from other extrachromosomal elements. Sequence analysis of CRISPR structures from 24 strains of Streptococcus thermophilus and Streptococcus vestibularis confirmed the homology of spacers with extrachromosomal elements. Phage sensitivity of S. thermophilus strains appears to be correlated with the number of spacers in the CRISPR locus the strain carries. The authors suggest that the spacer elements are the traces of past invasions by extrachromosomal elements, and hypothesize that they provide the cell immunity against phage infection, and more generally foreign DNA expression, by coding an anti-sense RNA. The presence of gene fragments in CRISPR structures and the nuclease motifs in cas genes of both cluster types suggests that CRISPR formation involves a DNA degradation step.