English: Space-fill drawing of the Cascade surveillance complex of the Type I CRISPR bacterial immune system from Escherichia coli. The multiple proteins of Cascade (in blue) all associate into a spiral, sea-horse-like shape around the crRNA guide strand (in orange) of a CRISPR-stored sequence from a previously invading virus, and search for the complementary DNA sequence in newly infecting viruses. That new DNA binds next to the RNA strand and is then chopped up. Drawn by David Goodsell from PDB entry 4tvx.