A novel prokaryotic immunity-like system (CRISPR/CAS) has been recently discovered (Barrangou et al., 2007; Brouns et al., 2008; Marraffini & Sontheimer, 2008), involving two main constituents: (i) clusters of regularly interspaced short palindromic repeats (CRISPR) and (ii) CAS (CRISPR-associated sequence) proteins.