Figure 1.

Schematics of the precursor CRISPR RNA (crRNA) and known RAMP proteins. (A) Upper panel shows features of the CRISPR RNA recognized by Cas6 that processes crRNA. “R” denotes repeat and “S” denotes spacer RNA. The darker red line depicts the region recognized by Cas6 and arrows indicate the cleavage site. Lower panel shows the names and sequences of the repeat RNA used in this study. “Ph” refers to P. horikoshii and “Pf” refers to P. furiosus. Black letters designate nucleotides that differ from those of Pf7 RNA. Note the close similarity between Ph5 and Pf7 RNA. (B) Schematic sequence features of the two RAMP proteins, Cas6 and Cas6nc (noncatalytic Cas6), and their cleavage activity on Pf7 RNA. The three red stripes on the schematic sequence indicate the three predicted catalytic residues of Cas6 that are lacking in Cas6nc. The substrate (30mer) and the product (22mer) are indicated by arrows. For each cleavage reaction, the enzyme concentration was 100 nM.