Figure 3.

Organization of CRISPR–Cas loci. (A) Number of CRISPR arrays in function of the number of cas clusters in bacterial genomes (mean, CI 95%). The straight line indicates the identity (number of CRISPRs equal to the number of cas clusters) (B) Frequency of CRISPRs and cas clusters in terms of their genetic context. Loci were classed as complete CRISPR–Cas loci when they included at least one CRISPR and one cas cluster, ‘distant’ when the element (CRISPR or cas cluster) is >20 kb from the closest cognate element, and ‘orphan’ when the cognate element is absent from the genome. (C) Quantification of the different organizations of CRISPR–Cas loci.