The database construction: from genomes to CRISPRs. The first step consists in downloading prokaryotic genomes which are then submitted to the CRISPRFinder program. The detected clusters are divided into two groups: confirmed CRISPRs (>=3DRs) are stored in the database; small questionable clusters (2 or 3 DRs) are analyzed by blasting their conserved region (DR) against the approved DRs; clusters with already identified DRs are added to the CRISPR database. Remaining questionable CRISPRs are analysed for classical flanking nucleotides and spacers length compared to the DR length. Clusters that do not fit these criteria are deleted, the remaining are kept as questionable. Manual discard of some sequences can be performed by the database curator. Colour code: programs are shown in blue, confirmed CRISPRs are in pink and questionable ones are in grey.