A Reverse Transcriptase-Cas1 Fusion Protein Contains a Cas6 Domain Required for CRISPR RNA processing and RNA Spacer Acquisition

Prokaryotic CRISPR-Cas systems provide adaptive immunity by integrating portions of invasive nucleic acids (spacers) between genomic CRISPR repeats. Cas6-family proteins help generate spacer-derived tags (crRNAs) that target Cas nucleases to matching invaders. We show that a Marinomonas mediterranea Cas6-reverse transcriptase (RT)-Cas1 fusion combines three biochemical activities (Cas6, RT, and Cas1) that function in both crRNA processing and spacer acquisition from RNA and DNA.