Fig. 2
From: Divergent methylation of CRISPR repeats and cas genes in a subtype I-D CRISPR-Cas-system
Four DNA methylation events can occur within the 5′- CGATCG − 3′ sequence that is at the core of the octameric HIP1 element. These methylations are carried out by the enzymes M.Ssp6803I (blue) and M.Ssp6803III (green) [7]. A 5′- CGATCG − 3′ recognition sequence is located within every single repeat of the Synechocystis 6803 CRISPR1 system. After transcription, this recognition sequence corresponds to four of the five nucleotides within the crRNA loop and to the two upper nucleotides of the right arm within the repeat stem-loop secondary structure that is essential for recognition by the Cas6–1 endoribonuclease, cleaving at the indicated site [20]