English: CRISPR-Cas9 Confers Adaptive Immunity. Left Panel: After a phage has injected its DNA into the bacterial cytoplasm, a protein complex forms consisting of Cas1 and Cas2. A sample sequence, termed protospacer, is acquired from the phage DNA by the Cas1-Cas2 complex (1). This sequence is then integrated into the CRISPR genetic locus (2). The sequence is now called a spacer. Several spacers from earlier contacts with phages are stored in the CRISPR genetic locus. Right Panel: Spacer sequences are transcribed as RNA, and Cas9 protein is synthesized (1). RNA binds to Cas9 to form a surveillance and interference complex (2). The complex then scans intracellular DNA for matching sequences (3). If a matching phage sequence is found, Cas9 destroys the DNA by cleavage (4).