Nearly all strains of Streptococcus agalactiae, the leading cause of invasive infections in neonates, encode a type II-A clustered regularly interspaced short palindromic repeats (CRISPR)-Cas system. Interestingly, S. agalactiae strains belonging to the hypervirulent Sequence Type 17 (ST17) contain significantly fewer spacers in their CRISPR locus than other lineages, which could be the result of a less functional CRISPR-Cas system. Here, we revealed one large deletion in the ST17 cas promoter region and we evaluated its impact on the transcription of cas genes as well as the functionalities of the CRISPR-Cas system. We demonstrated that Cas9 interference is functional and that the CRISPR-Cas system of ST17 strains can still acquire new spacers, despite the absence of a regular cas promoter. We demonstrated that a promoter sequence upstream of srn036, a small RNA partially overlapping the antisense tracrRNA, is responsible for the ST17 CRISPR-Cas adaptation and interference activities.

中文翻译：

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无乳链球菌高毒株II-A型CRISPR-Cas系统的功能研究

几乎所有无乳链球菌菌株（新生儿侵袭性感染的主要原因）都编码 II-A 型成簇规则间隔短回文重复序列 (CRISPR)-Cas 系统。有趣的是，属于超毒力序列 17 型 (ST17) 的无乳链球菌菌株在其 CRISPR 基因座中包含的间隔区比其他谱系少得多，这可能是功能较弱的 CRISPR-Cas 系统的结果。在这里，我们揭示了 ST17 cas启动子区域的一个大缺失，并评估了它对cas转录的影响基因以及 CRISPR-Cas 系统的功能。我们证明了 Cas9 干扰是有功能的，并且 ST17 菌株的 CRISPR-Cas 系统仍然可以获得新的间隔区，尽管没有常规的cas启动子。我们证明了srn036上游的启动子序列，一种与反义 tracrRNA 部分重叠的小 RNA，负责 ST17 CRISPR-Cas 适应和干扰活动。