In prokaryotes, clustered regularly interspaced short palindromic repeat (CRISPR) loci encode small CRISPR RNAs (crRNA) that protect against invasive genetic elements. These crRNAs are used as guides by various CRISPR associated (Cas) proteins to target foreign genetic elements and are the bases of a prokaryotic defense system that preserves the host genome. The Cas module RAMP (Cmr) proteins form a complex that is unique amongst the CRISPR/Cas systems for its ability to target and cleave RNA, whereas the other systems target DNA. The Cmr complex is composed of 6 protein subunits, named Cmr1-6, and a crRNA. Our goal is to understand the roles of the individual Cmr subunits and their interactions in the complex using biochemical and structural approaches. It is important to understand these fundamental properties of CRISPR/Cas complexes because of their central role in prokaryotic immunity and our lack of knowledge in this important pathway. Upon better understanding, we hope that manipulation of this natural pathway may be used to impair the spread of antimicrobial resistance factors. It has been demonstrated that the CRISPR/Cas system is able to limit horizontal gene transfer, which is the main route for bacteria to acquire resistance, by targeting the degradation of conjugative plasmids. A role can be conceived whereby specifically Cmr can be used silence RNA transcripts that may code for proteins that facilitate HGT. Such developments may have considerable public health applications and would be consistent with the NIH goals of advancing our understanding of biological systems, controlling disease and improving human health.

Public Health Relevance

The main route for bacteria to acquire bacterial resistance is through horizontal gene transfer (HGT), it is a mechanism used to exchange genetic material between bacteria. To limit their spread, we must develop new technologies to target HGT. Clustered regularly interspaced short palindromic repeats (CRISPR) is a novel prokaryotic immune system found in bacteria that targets foreign genetic material. Using biochemistry and structural biology we are trying to characterize a CRISPR targeting pathway and upon better understanding, we hope that manipulation of this natural pathway may be used to impair the spread of antimicrobial resistance by limiting HGT.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Predoctoral Individual National Research Service Award (F31)
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Special Emphasis Panel (ZRG1)
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Gaillard, Shawn R
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Johns Hopkins University
Schools of Public Health
United States
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Estrella, Michael A; Kuo, Fang-Ting; Bailey, Scott (2016) RNA-activated DNA cleavage by the Type III-B CRISPR-Cas effector complex. Genes Dev 30:460-70