CRISPR-Cas是原核生物用来抵御病毒等外源遗传物质入侵的一种获得性免疫系统；其免疫适应是将异己DNA加工、整合到CRISPR位点形成新间隔序列的过程。申报人最新成果揭示Csa3a是激活嗜热古菌硫化叶菌I-A型CRISPR-Cas系统原发适应（de novo adaptation）的关键调控蛋白（Liu et al., 2015, NAR）。但在该系统中参与外源DNA加工、整合等步骤的必需蛋白尚未得到鉴定和系统的功能研究。在此项目中申请人将鉴定硫化叶菌I-A系统参与原发适应的必需Cas和DNA复制、修复蛋白，研究其在该过程中加工、整合外源DNA和聚合DNA缺口的功能。并分析原发适应必需的Cas蛋白造成CRISPR-Cas或靶标DNA突变的规律。通过该项目研究，我们将揭示硫化叶菌I-A系统在原发适应过程中Cas蛋白与DNA复制、修复蛋白的协调工作机制，及必需Cas蛋白介导的逃逸突变机制。

CRISPR-Cas system encodes the prokaryotic adaptive immune system that provides immunity against the invasion by mobile genetic elements. The adaptation process of CRISPR-Cas system acquires new spacers from non-self DNA into CRISPR arrays. The applicant’s recent study reveals Csa3a is the crucial transcriptional regulator activating CRISPR de novo adaptation in the archaeon Sulfolobus (Liu et al., 2015, Nucleic Acids Res). But the mechanisms involved in the process remains elusive. For example, proteins essential for de novo adaptation and their specific functions in this process have not been systematically studied. Base on our own results, we will identify the essential Cas proteins, DNA polymerases and DNA repair proteins, and study their specific functions on de novo adaptation of foreign DNA into CRISPR arrays. We will further identify the proteins involved in de novo adaptation-mediated immune escape and characterize the mutation properties at CRISPR-Cas loci or protospacer regions. The research aims to reveal the specific functions and cooperation of the essential adaptation Cas, DNA polymerase and DNA repair proteins, and discovery the rules controlling the immune escape mutation during de novo adaptaion process in Sulfolobus Type I-A CRISPR-Cas system.