A series of advances have been made in the adaptation mechanism of CRISPR, where microorganisms are located.

CRISPRs-Cas systems are adaptive nucleic acid immune systems that are widely found in bacteria and germs.
The system has a wide variety of functional components and nucleic acid processing mechanisms, providing humans with the most efficient genome editing techniques to date (such as CRISPR-Cas9) and genetic testing techniques (such as CRISPR-C2c2/Cas13a), as well as a cutting-edge window for understanding the evolution and adaptation mechanisms of life.
The National Key Laboratory for The Early Development of Microbiological Resources of the Institute of Microbiology of the Chinese Academy of Sciences to China Research Group is an early team engaged in basic research on CRISPR-Cas system in China, and in the face of the long-standing international shortage of CRISPR adaptation system to obtain spacer efficiently from pure viruses, the first (second of all systems) CRISPR-Cas system was established in 2014 in the paleobacterial system for the efficient adaptation of pure viruses, revealing the salt-like bacteria I-BCRISPR The essence of "triggering" the need for efficient adaptation has for the first time raised the important argument that triggering adaptation may be the main mode of efficient adaptation of viruses in nature by CRISPR systems, and further discovering that, in addition to efficiency, trigger adaptation also enables strict alien differentiation and efficient antivirus escape mechanism through clever PAM validation, answering the problems of efficiency and heterogeneity in the adaptation process that has plagued scientists for many years (Nuiccle Acid Res. 2014, 42:2483-2492; Nucleic Acids Res., 2014, 42:7226-7235).
work has been cited more than 80 times by Nature, Cell, Science, PNAS, etc. as an important discovery in the field of CRISPR adaptation.
recently, through the manual alteration of the CRISPR system, the Research Group in China has made continuous new progress in the length of spacer decisions and site recognition mechanisms for fixed-point integration during CRISPR adaptation (Nucleic Acids Res., 2016, 44:4266-4277; Nucleics Acid Res., 2017, 45:4642-4654).
the CRISPR adaptation process, spacer integration reactions often occur at the leader end of the CRISPR structure and are accurately replicated at the repeat adjacent to it.
has long been widely believed that integrated complexes identify one end of the repeat first and then the other end through a rigorous molecular scale mechanism to determine the size and sequence of the newly copied repeat.
but interestingly, multiple research teams tend to identify the "repeat nearleader" end of the sequence first, while others believe that the "repeat far leader" end is identified first.
to China Research Group cleverly designed a trigger-integration separation CRISPR efficient adaptation system, through the system's scanning mutation identified two key integrated identification elements inside repeat.
, component 1 (AACCC) is strictly located at 10 bp downstream of the "near leader" end integration point, while the "far leader" end integration reaction occurs strictly at about 10 bp downstream of component 2 (GTGGG).
The above two components are necessary for repeat recognition, and the increase or decrease of spacing can be correspondingly increased or decreased within a certain range of the inherent size of repeat, which indicates that there is no repeat length molecular scale mechanism in the spacer integration process, but the integration complex first identifies nearlea The internal key components of the repeat of the der identify the integrated reaction site at both ends by a molecular ruler of about 10-bp (Nucleic Acids Res., 2016, 44:4266-4277).
interestingly, this important discovery was published shortly after it was quickly supported by experimental data from other international teams in E. coli, indicating that the mechanism is universal in different CRISPR systems.
Regarding the spacer length decision mechanism, in 2016 two major international laboratories analyzed the crystal structure of the E. coli Spacer Acquisition Machine (Cas1-Cas2 complex) in a substrate binding state almost simultaneously, and they found that the structural limitations of the complex provided a fixed molecular scale and defined the length of spacer.
but inspiciently, in most other CRISPR systems, spacer lengths are not fixed, but have a certain dimensional polymorphism.
further designed a CRISPR single-induced adaptation system to the Chinese research team, using high-volume sequencing technology, analyzed the acquisition process of nearly 40,000 new spacer, and found that, like the data already available in nature, the dimensions of these spacers are not fixed, but in a certain range of normal distribution.
interestingly, they detected cytosine (C) preferences at the penultimate base point of spacer through bioinformic analysis, and mutations at the corresponding bits changed the size of the acquired spacer.
This high-volume data combined with molecular genetics experimental analysis, it was found for the first time that the spacer acquisition machine not only identified the PAM sequence on the side of the protospacer 5' side, but also identified the partial sequence of the protospacer 3' end, which specifically identified the mechanism of the molecular scale of the acquisition machine to fine-tune, resulting in the polymorphism of the spacer size.
the big data analysis obtained by spacer also observed the slip of the adaptation machine on the virus template and the flip during integration, and further demonstrated the sliding hypothesis of two-way search for spacer during adaptation (Nucleic Acids Res., 2017, 45:4642-4654).
These latest developments provide a new basis for the system to understand the efficiency and specificity of CRISPR-triggered adaptation processes (targeting, bidirectional seeking, fixed-point integration) (Figure 1) and for the future development of molecular biology techniques based on CRISPR's subtle adaptation processes.
Li Ming and Yu Luyao of the Chinese team are the first co-authors of Nucleic Acids Res., 2017, 45:4642-4654;
related research has been funded by the National Natural Science Foundation of China (the project on the surface).
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