All cellular organisms have developed strategies to combat parasitic genome invaders. In many bacteria and most archaea, CRISPR ( Clustered Regularly Interspaced Short Palindromic Repeats)-Cas ( CRISPR- associated proteins) has recently emerged as an adaptive RNA-mediated defense mechanism that provides cells with acquired resistance to invading foreign genetic elements such as bacteriophages and plasmids
- Differential Diagnosis in Clinical Medicine 1st Edition PDF Free
- Textbook of Dental Anatomy and Oral Physiology PDF Free
- ENT An Introduction and Practical Guide 2nd Edition 2018 PDF Free
- Practice Questions for NCLEX-PN (Test Preparation) 2nd Edition PDF Free
- The ADA Practical Guide to Soft Tissue Oral Disease 2nd Edition 2018 PDF Free
These defense systems are composed of Cas proteins, and one or more CRISPR arrays containing a collec-
tion of short repeat-spacer sequences that provide the CRISPR RNAs (crRNAs) that target the foreign genome. Immunity to invading genomes is mediated via a three-stage process: (1) adaptation via acquisition of viral or plasmid DNA-derived spacers into the CRISPR array, (2) expression and maturation of the short crRNAs, and (3) interference with the invading cognate foreign genomes.
The repeat-spacer CRISPR array contents and cas genes have undergone an extraordinarily dynamic rate of evolution leading to a complex diversity in the genetic architectures of the CRISPR-Cas systems. Indeed, currently there are three major types (I–III) consisting of more than 11 subtypes. Although the general principles of the three-stage immunity process are conserved, CRISPR-Cas has evolved a wide variety of precise and coordinated mechanisms that are mainly based on the Cas proteins involved. Interestingly, recent struc-
tural studies of Cas protein interference complexes in type I and III systems have demonstrated an overall similarity in architecture, despite a large difference in subunit sequence and composition.
CRISPR-Cas adaptive immune systems are currently one of the most fl ourishing and fascinating research themes in microbiology and much work has been performed in the last 10 years. Important fi ndings have recently been made towards the understanding of the molecular mechanisms of CRISPR-Cas systems mediating crRNA expression and interference in many select CRISPR-Cas systems. In the last couple of years, we have also witnessed a rapid growth in our understanding of the process of spacer acquisition, although the
mechanistic details are largely unknown. Other details around, for example, CRISPR-Cas regulation and the role of the systems in other processes remain obscure.
By their remarkable mechanistic and functional diversity, CRISPR-Cas systems constitute an extraordinary source of proteins for RNA-DNA, DNA-protein, RNA-protein, and protein-protein interactions that can be developed for applied use. The applications are diverse and include the ability to repress or activate the transcription of genes of interest. The best known application to date is genome editing based on the type II CRISPR-Cas9 system.
It is not an overstatement that the ability to use a single Cas9 protein with a guide RNA to direct sitespecifi c cleavage of target DNA has revolutionized genome engineering in organisms ranging from bacteria and yeast to plants and animals. The therapeutic potential of CRISPR-Cas9 has been demonstrated by, e.g., curing genetic defects in adult mice, and there is a large interest in developing CRISPR-Cas9 for gene therapy in humans. These advances have resulted in the CRISPR-Cas9 technology being adopted as a common genetic tool in the scientifi community in a very short time.
Free Books Online PDF: CRISPR: Methods and Protocols – 2015