FIG 8.

Summary of experimentally studied conserved amino acid residues of Cas4 family proteins involved in the functions of CRISPR spacer acquisition. (A) Experimentally characterized amino acid residues in Cas4 family proteins, using the Cas4 (SiRe_0763) protein from S. islandicus REY15A. Conserved residues represented by black lines and letters were identified by Shiimori et al. (30), and conserved residues represented by green lines and letters were examined in this study. (B) Functions of the experimentally characterized amino acid residues in the RecB nuclease motif of Cas4 proteins. Weak to strong influences are indicated by + to +++, and no influence is indicated by −. D70 and H91 have functions in Cas4-1 and Cas4-2 from P. furiosus (30).