As befits an immune mechanism, CRISPR-Cas systems are highly variable with respect to Cas protein sequences, gene composition, and organization of the genomic loci. Optimal classification of CRISPR-Cas systems and rational nomenclature for CRISPR-associated genes are essential for further progress of CRISPR research. These are highly challenging tasks because of the complexity of CRISPR-Cas and their fast evolution, including frequent module shuffling, as well as the lack of universal markers for a consistent evolutionary classification. The complexity and variability of CRISPR-Cas systems necessitate a multipronged approach to classification and nomenclature. We present a brief summary of the current state of the art and discuss further directions in this area.

中文翻译：

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CRISPR-Cas系统的分类和术语：从哪里来？

作为一种免疫机制，CRISPR-Cas系统在Cas蛋白序列，基因组成和基因组基因座的组织方面具有很大的可变性。CRISPR-Cas系统的最佳分类和CRISPR相关基因的合理命名对于CRISPR研究的进一步发展至关重要。由于CRISPR-Cas的复杂性及其快速进化（包括频繁的模块改组）以及缺乏用于一致的进化分类的通用标记，这些都是极具挑战性的任务。CRISPR-Cas系统的复杂性和可变性要求采用多管齐下的分类和命名方法。我们将简要介绍当前的技术现状，并讨论该领域的进一步发展方向。