CRISPR-Cas immunity: analysis of adaptation and interference reactions in prokaryotesTools Cass, S.D.B. (2016) CRISPR-Cas immunity: analysis of adaptation and interference reactions in prokaryotes. PhD thesis, University of Nottingham.
AbstractMobile genetic elements (MGEs, e.g. transposons, plasmids and phage) are an important driver of genetic diversity in microorganisms, and have diverse effects on microbe populations. Adaptation of Bacteria and Archaea to overcome negative effects of phage infection is sometimes referred to as an “arms race” that provokes the development of systems to protect against phage attack. One such defence is CRISPR-Cas, the topic of this research thesis. CRISPR (Clustered Regular Interspersed Short Palindromic Repeat) loci and Cas (CRISPR-associated) proteins are the molecular basis of this resistance mechanism. CRISPR-Cas can protect against phage and other foreign MGEs by incorporating a fragment of novel DNA into CRISPR (spacer acquisition) and using this as a template to generate a small RNA molecule, CRISPR RNA (crRNA), which targets the degradation of complementary sequences (interference). Effective interference requires formation of R-loop nucleic acid structure of crRNA base-pairing to homologous DNA, at positions flanked by PAM (Protospacer Adjacent Motif) sequence within the invader.
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