Journal Article

Direct CRISPR spacer acquisition from RNA by a natural reverse transcriptase–Cas1 fusion protein

Markham, Laura M., Sanchez-Amat, Antonio, Lambowitz, Alan M., Silas, Sukrit, Sidote, David J., Bhaya, Devaki, Mohr, Georg, Fire, Andrew Z.

2016

Overview

The CRISPR (clustered regularly interspaced short palindromic repeat) system provides bacteria with an adaptive immune response. DNA captured from viruses and plasmids by CRISPR-associated protein 1 (Cas1) is used by bacteria to target the invaders' for destruction. Silas et al. discover that certain classes of the Cas1 gene are fused to a reverse transcriptase gene ( RT-Cas1 ) (see the Perspective by Sontheimer and Marraffini). These RT-Cas1 proteins are able to capture and directly incorporate both DNA and RNA into CRISPR loci. RT-Cas1 systems could be effective against parasitic RNA species, or even to modulate bacterial gene expression. Science , this issue p. 10.1126/science.aad4234 ; see also p. 920 A reverse transcriptase activity captures and introduces RNA directly into CRISPR loci. CRISPR systems mediate adaptive immunity in diverse prokaryotes. CRISPR-associated Cas1 and Cas2 proteins have been shown to enable adaptation to new threats in type I and II CRISPR systems by the acquisition of short segments of DNA (spacers) from invasive elements. In several type III CRISPR systems, Cas1 is naturally fused to a reverse transcriptase (RT). In the marine bacterium Marinomonas mediterranea (MMB-1), we showed that a RT-Cas1 fusion protein enables the acquisition of RNA spacers in vivo in a RT-dependent manner. In vitro, the MMB-1 RT-Cas1 and Cas2 proteins catalyze the ligation of RNA segments into the CRISPR array, which is followed by reverse transcription. These observations outline a host-mediated mechanism for reverse information flow from RNA to DNA.

• Publisher: American Association for the Advancement of Science,The American Association for the Advancement of Science
• Subject: Bacteria / Bacterial proteins / Bacterial Proteins - classification / Bacterial Proteins - genetics / Bacterial Proteins - metabolism / Base Sequence / Clustered Regularly Interspaced Short Palindromic Repeats / CRISPR-Associated Proteins - classification / CRISPR-Associated Proteins - genetics / CRISPR-Associated Proteins - metabolism / CRISPR-Cas Systems / Deoxyribonucleic acid / DNA / DNA - genetics / Genomics / Immune response / Immune system / Inactivation / Information Transfer / Introns - genetics / Marinomonas - enzymology / Marinomonas - genetics / Molecular Sequence Data / Mutant Chimeric Proteins - classification / Mutant Chimeric Proteins - genetics / Mutant Chimeric Proteins - metabolism / Mutation / Parasites / Phylogeny / Protein Structure, Tertiary / Proteins / RESEARCH ARTICLE SUMMARY / Ribonucleic acid / RNA / RNA - genetics / RNA - metabolism / RNA Splicing / RNA-Directed DNA Polymerase - classification / RNA-Directed DNA Polymerase - genetics / RNA-Directed DNA Polymerase - metabolism