title: CRISPR-Cas Adaptive Immune Systems of the Sulfolobales: Unravelling Their Complexity and Diversity.
abstract: The Sulfolobales have provided good model organisms for studying CRISPR-Cas systems of the crenarchaeal kingdom of the archaea. These organisms are infected by a wide range of exceptional archaea-specific viruses and conjugative plasmids, and their CRISPR-Cas systems generally exhibit extensive structural and functional diversity. They carry large and multiple CRISPR loci and often multiple copies of diverse Type I and Type III interference modules as well as more homogeneous adaptation modules. These acidothermophilic organisms have recently provided seminal insights into both the adaptation process, the diverse modes of interference, and their modes of regulation. The functions of the adaptation and interference modules tend to be loosely coupled and the stringency of the crRNA-DNA sequence matching during DNA interference is relatively low, in contrast to some more streamlined CRISPR-Cas systems of bacteria. Despite this, there is evidence for a complex and differential regulation of expression of the diverse functional modules in response to viral infection. Recent work also supports critical roles for non-core Cas proteins, especially during Type III-directed interference, and this is consistent with these proteins tending to coevolve with core Cas proteins. Various novel aspects of CRISPR-Cas systems of the Sulfolobales are considered including an alternative spacer acquisition mechanism, reversible spacer acquisition, the formation and significance of antisense CRISPR RNAs, and a novel mechanism for avoidance of CRISPR-Cas defense. Finally, questions regarding the basis for the complexity, diversity, and apparent redundancy, of the intracellular CRISPR-Cas systems are discussed.
authors.affiliation: Archaea Centre, Department of Biology, Copenhagen University, Ole Maaløes Vej 5, DK2200 Copenhagen N, Denmark. garrett@bio.ku.dk.
authors.forename: Roger A
authors.initials: RA
authors.lastname: Garrett
authors.affiliation: Archaea Centre, Department of Biology, Copenhagen University, Ole Maaløes Vej 5, DK2200 Copenhagen N, Denmark. sashah@bio.ku.dk.
authors.forename: Shiraz A
authors.initials: SA
authors.lastname: Shah
authors.affiliation: School of Biotechnology and Biomolecular Sciences, University of New South Wales, 2052 Sydney NSW, Australia. s.erdmann@unsw.edu.au.
authors.forename: Susanne
authors.initials: S
authors.lastname: Erdmann
authors.affiliation: Archaea Centre, Department of Biology, Copenhagen University, Ole Maaløes Vej 5, DK2200 Copenhagen N, Denmark. liuguannan@bio.ku.dk.
authors.forename: Guannan
authors.initials: G
authors.lastname: Liu
authors.affiliation: Archaea Centre, Department of Biology, Copenhagen University, Ole Maaløes Vej 5, DK2200 Copenhagen N, Denmark. mmousaei@bio.ku.dk.
authors.forename: Marzieh
authors.initials: M
authors.lastname: Mousaei
authors.affiliation: Archaea Centre, Department of Biology, Copenhagen University, Ole Maaløes Vej 5, DK2200 Copenhagen N, Denmark. clsobrino@bio.ku.dk.
authors.forename: Carlos
authors.initials: C
authors.lastname: León-Sobrino
authors.affiliation: Archaea Centre, Department of Biology, Copenhagen University, Ole Maaløes Vej 5, DK2200 Copenhagen N, Denmark. wenfang.peng@bio.ku.dk.
authors.forename: Wenfang
authors.initials: W
authors.lastname: Peng
authors.affiliation: Archaea Centre, Department of Biology, Copenhagen University, Ole Maaløes Vej 5, DK2200 Copenhagen N, Denmark. soley.gudbergsdottir@bio.ku.dk.
authors.forename: Soley
authors.initials: S
authors.lastname: Gudbergsdottir
authors.affiliation: Archaea Centre, Department of Biology, Copenhagen University, Ole Maaløes Vej 5, DK2200 Copenhagen N, Denmark. lingd@bio.ku.dk.
authors.forename: Ling
authors.initials: L
authors.lastname: Deng
authors.affiliation: Helmholtz Zentrum München, Research Unit Environmental Genomics, Ingolstädter Landstraße 1, 85764 Oberschleißheim, Germany. gisle.vestergaard@helmholtz-muenchen.de.
authors.forename: Gisle
authors.initials: G
authors.lastname: Vestergaard
authors.affiliation: Archaea Centre, Department of Biology, Copenhagen University, Ole Maaløes Vej 5, DK2200 Copenhagen N, Denmark. peng@bio.ku.dk.
authors.forename: Xu
authors.initials: X
authors.lastname: Peng
authors.affiliation: Archaea Centre, Department of Biology, Copenhagen University, Ole Maaløes Vej 5, DK2200 Copenhagen N, Denmark. qunxin@bio.ku.dk.
authors.forename: Qunxin
authors.initials: Q
authors.lastname: She