CRISPR + CAS = Defensive or Immune System CRISPR: Clustered Regulatory Interspaced Short Palindromic Repeats Region of bacterial chromosome containing DNA sequences similar to foreign DNA (spacers) alternating with identical repeated sequences (Figure 10.28) CRISPR-associated proteins (Cas proteins) Obtain and store segments of foreign DNA as spacers Recognize and destroy foreign DNA

Figure 10.28 Figure 10.28 Operation of the CRISPR system. Unique spacer sequences Bacterial chromosome DNA cas genes Repeat Repeat Cas proteins Transcription and translation Transcription CRISPR RNA Cutting of RNA by Cas proteins Foreign sequence is recognized by CRISPR RNA. Figure 10.28 Operation of the CRISPR system. Viral infection or conjugation Viral or plasmid DNA Cas proteins cut and destroy foreign nucleic acid. Figure 10.28