CRISPR-Cas (clustered regular intervals of short palindromic repeat sequences and their associated proteins) can be divided into two classes, Class I is the use of multiple Cas protein, and CRISPR RNA (crRNA) formation effect complex, class II system Simpler, is the use of a large single-effect crRNA-mediated interference.
In a recent paper, the famous CRISPR research pioneer: Zhang Feng led a research team using the calculation of the sequence database mining method, found two types of CRISPR-Cas system -subtype VI-B, the system lacks Cas1 and Cas2, contains a single large effector protein Cas13b, and two previously unrelated proteins: Csx27 and Csx28. The analysis of the characteristics of these new systems will help develop new tools for manipulating and monitoring cell transcription processes.
The study was published in the February 16 issue of Molecular Cell magazine, the author of the article is Professor Broad Professor of Broad Research Institute, he was promoted to MIT history last year, the youngest Chinese lifetime professor, this year he became the first Professor James and Patricia Poitras of MIT.
The CRISPR-Cas system is an acquired immune system for bacteria that protects microorganisms from exogenous nucleic acids by RNA-directed endonucleases. CRISPR-Cas system also has important and basic biological significance, despite the great concern and interest that CRISPR has caused due to important applications in genome editing. And it is worth noting that the unique mechanisms of these immune systems make them a simple and easy genetic engineering tool. It can be said that the most striking aspect of the CRISPR-Cas function is that this is the only known example of "adaptive immunity with inheritable genomic memory", the mechanism by which Ramak's adaptive character is inherited.
CRISPR system has many types, in which the VI type CRISPR-Cas system is closely related to microbial immunity and programmed cell organisms. Studies have shown that the VI effect protein contains two HEPN domains and is expected to have RNase activity, which requires two HEPN structures Domain activity has actually been demonstrated in the subtype VI-A effector (Cas13a).
In the latest article, Zhang Feng research group using a data mining method, found two subtypes VI-B CRISPR-Cas system. The researchers found that these CRISPR-Cas systems could achieve heterologous expression of RNA interference. Through further biochemical and genetic experiments, they found that Cas13b used short and long direct repeat fragments to complete its own CRISPR array, excised target RNA, completed RNase active.
In addition, the researchers also screened the essential genes of the target by screening for the essential gene of Escherichia coli, demonstrating that Cas13b has a double-stranded pre-banding sequence. While Csx27 inhibits the Csx28 enhancer, but the Cas13b-mediated RNA interference. The characterization of these CRISPR systems helps to develop new tools for manipulating and monitoring cellular transcription processes.