Specificity logos and frequency matrices present the user with a visual representation of peptidase specificity. An example specificity logo is shown in Figure 2 . From the logo and the cleavage pattern string it is clear that caspase-3 has an absolute requirement for Asp in the S1 pocket (position 4, only one cleavage after Glu is known) and a preference for Asp in S4. There are minor preferences for Glu in S3 and Gly or Ser in S1 0 .