Laboratory of Bacteriology, The Rockefeller University, New York, NY 10065, USA.
Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA.
Cell Host Microbe. 2019 Feb 13;25(2):242-249.e3. doi: 10.1016/j.chom.2018.12.016. Epub 2019 Jan 29.
CRISPR-Cas systems provide acquired immunity in prokaryotes. Upon infection, short sequences from the phage genome, known as spacers, are inserted between the CRISPR repeats. Spacers are transcribed into small RNA molecules that guide nucleases to their targets. The forces that shape the distribution of newly acquired spacers, which is observed to be uneven, are poorly understood. We studied the spacer patterns that arise after phage infection of Staphylococcus aureus harboring the Streptococcus pyogenes type II-A CRISPR-Cas system. We observed that spacer patterns are established early during the CRISPR-Cas immune response and correlate with spacer acquisition rates, but not with spacer targeting efficiency. The rate of spacer acquisition depended on sequence elements within the spacer, which in turn determined the abundance of different spacers within the adapted population. Our results reveal how the two main forces of the CRISPR-Cas immune response, acquisition and targeting, affect the generation of immunological diversity.
CRISPR-Cas 系统为原核生物提供获得性免疫。在感染期间，噬菌体基因组中的短序列，称为间隔序列，被插入 CRISPR 重复序列之间。间隔序列被转录为小 RNA 分子，指导核酸酶靶向其靶标。然而，新获得的间隔序列分布不均匀的形成机制尚不清楚。我们研究了在携带链球菌 II-A 型 CRISPR-Cas 系统的金黄色葡萄球菌中噬菌体感染后出现的间隔序列模式。我们观察到，间隔序列模式在 CRISPR-Cas 免疫反应的早期就已经建立，并与间隔序列获取率相关，但与间隔序列靶向效率无关。间隔序列的获取率取决于间隔序列内的序列元件，这些元件反过来又决定了适应种群中不同间隔序列的丰度。我们的结果揭示了 CRISPR-Cas 免疫反应的两个主要力量，即获取和靶向，如何影响免疫多样性的产生。
