CRISPR-mediated defense mechanisms in the hyperthermophilic archaeal genus Sulfolobus.

CRISPR (clustered regularly interspaced short palindromic repeats)-mediated virus defense based on small RNAs is a hallmark of archaea and also found in many bacteria. Archaeal genomes and, in particular, organisms of the extremely thermoacidophilic genus Sulfolobus, carry extensive CRISPR loci each with dozens of sequence signatures (spacers) able to mediate targeting and degradation of complementary invading nucleic acids. The diversity of CRISPR systems and their associated protein complexes indicates an extensive functional breadth and versatility of this adaptive immune system. Sulfolobus solfataricus and S. islandicus represent two of the best characterized genetic model organisms in the archaea not only with respect to the CRISPR system. Here we address and discuss in a broader context particularly recent progress made in understanding spacer recruitment from foreign DNA, production of small RNAs, in vitro activity of CRISPR-associated protein complexes and attack of viruses and plasmids in in vivo test systems.