Function and Regulation of Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) / CRISPR Associated (Cas) Systems

Abstract

Phages are the most abundant biological entities on earth and pose a constant challenge to their bacterial hosts. Thus, bacteria have evolved numerous ‘innate’ mechanisms of defense against phage, such as abortive infection or restriction/modification systems. In contrast, the clustered regularly interspaced short palindromic repeats (CRISPR) systems provide acquired, yet heritable, sequence-specific ‘adaptive’ immunity against phage and other horizontally-acquired elements, such as plasmids. Resistance is acquired following viral infection or plasmid uptake when a short sequence of the foreign genome is added to the CRISPR array. CRISPRs are then transcribed and processed, generally by CRISPR associated (Cas) proteins, into short interfering RNAs (crRNAs), which form part of a ribonucleoprotein complex. This complex guides the crRNA to the complementary invading nucleic acid and targets this for degradation. Recently, there have been rapid advances in our understanding of CRISPR/Cas systems. In this review, we will present the current model(s) of the molecular events involved in both the acquisition of immunity and interference stages and will also address recent progress in our knowledge of the regulation of CRISPR/Cas systems.

Novel configurations of type I and II CRISPR–Cas systems in Corynebacterium diphtheriae

“…Several factors including restriction-modification systems and CRISPR-Cas systems are involved in regulating gene flow between strains by providing immunity against the invading DNA. CRISPR-Cas-mediated immunity is particularly interesting because it involves acquisition of the spacer sequence from the invading DNA, which is used for future identification and degradation by cas-encoded nucleases (Bhaya et al, 2011;Fineran & Charpentier, 2012;Richter et al, 2012). C. diphtheriae strains possess three CRISPR-Cas systems, two of which are variants of the previously reported type I-E system (Makarova et al, 2011) and the third has recently been designated type II-C (Chylinski et al, 2013).…”

“…Clustered regularly interspaced short palindromic repeats (CRISPRs) are one of the major barriers to recombination and provide immunity to host cells against invading nucleic acids, such as phage and plasmids (Bhaya et al, 2011;Fineran & Charpentier, 2012;Richter et al, 2012). CRISPR-associated proteins (Cas) and CRISPRs (CRISPRCas) systems are composed of cas genes and one or more CRISPR arrays that consist of short unique spacers separated by repeat sequences of a similar size (Bhaya et al, 2011).…”

A fast and reliable method for monitoring of prophage‐activating chemicals

“…They influence biogeochemical cycles (e.g. by the release of nutrients of lysed bacteria), and as a result, they are able to shape the composition and structure of the microbial community (Hambly and Suttle, 2005; Paul, 2008; Thingstad et al ., 2008; Rohwer and Thurber, 2009; Richter et al ., 2012; Aziz et al ., 2015; Howard‐Varona et al ., 2017). Phages can multiply in their hosts by two different life cycle strategies.…”

A CRISPR-Cas system enhances envelope integrity mediating antibiotic resistance and inflammasome evasion

“…gene regulation | innate immune evasion C lustered, regularly interspaced, short palindromic repeats-CRISPR associated (CRISPR-Cas) systems are adaptive bacterial defenses against foreign nucleic acids derived from bacteriophages, plasmids, and other sources (1)(2)(3)(4). Foreign nucleic acids are targeted by direct hybridization of small CRISPR RNAs (crRNAs), which act in conjunction with conserved Cas proteins to mediate cleavage of the target.…”