CRISPR-Cas systems are adaptive immunity that is present in the majority of archaea, about 90 percent, and almost half of the bacteria. CRISPR-Cas can capture fragments which are originated from invasive DNA sequences (spacers), such as viruses, bacteriophage for bacteria or plasmids and create a sequence-based array for cleaving viral mobile elements, and also ancillary DNA that can be either taken by transformation, natural acquisition and transduction or also target self chromosome or plasmids that are presented inside the cell. Characterization and study the evolution of CRISPR-Cas systems not only provided a better understanding of defense mechanisms in prokaryotes but also is necessary knowledge for genome editing.
CRISPR-Cas systems are under rapid evolution, and due to the additional horizontal gene transfer events, there are different combinations of Cas proteins that give rise to multiple types of CRISPR-Cas systems. Therefore, it is quite challenging to study all these diversities from an evolutionary point of view. The aim of this project is to discover the diversity and distribution of different varieties of CRISPR-Cas systems based on their effector complex (Cas proteins) across the phylogenetic tree.
We were able to identify different functional clusters of the Cas-related proteins. We showed that multiple clusters are present in major phyla, implying a high degree of HGT, and at the same time we found phyla associated with single clusters that may have evolved in isolation from bacteriophages. Presentation_S. Nassirnia (slides)