The principal function of archaeal and bacterial CRISPR-Cas systems is antivirus adaptive immunity. However, recent genome analyses identified a variety of derived CRISPR-Cas variants at least some of which appear to perform different functions. Here, we describe a unique repertoire of CRISPR-Cas-related systems that we discovered by searching archaeal metagenome-assemble genomes of the Asgard superphylum. Several of these variants contain extremely diverged homologs of Cas1, the integrase involved in CRISPR adaptation as well as casposon transposition. Strikingly, the diversity of Cas1 in Asgard archaea alone is greater than that detected so far among the rest of archaea and bacteria. The Asgard CRISPR-Cas derivatives also encode distinct forms of Cas4, Cas5, and Cas7 proteins, and/or additional nucleases. Some of these systems are predicted to perform defense functions, but possibly not programmable ones, whereas others are likely to represent previously unknown mobile genetic elements.

中文翻译：

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Asgard Archaea 中独特的 CRISPR-Cas 相关系统和 Cas1 同源物的前所未有的多样性

古细菌和细菌 CRISPR-Cas 系统的主要功能是抗病毒适应性免疫。然而，最近的基因组分析发现了多种衍生的 CRISPR-Cas 变体，其中至少有一些似乎具有不同的功能。在这里，我们描述了我们通过搜索 Asgard superphylum 的古菌宏基因组组装基因组发现的 CRISPR-Cas 相关系统的独特曲目。其中一些变体包含 Cas1、参与 CRISPR 适应和 casposon 转座的整合酶的极其不同的同源物。引人注目的是，仅在 Asgard 古菌中 Cas1 的多样性就大于目前在其他古菌和细菌中检测到的多样性。Asgard CRISPR-Cas 衍生物还编码不同形式的 Cas4、Cas5 和 Cas7 蛋白和/或其他核酸酶。