The most immediate thing to note is just how widespread CRISPR is as a process used by cellular life. About 40% of all studied bacteria have the system in their genome, but that’s practically nothing compared to Archaea, where 90% of all those studied have it. They just lose out overall due to having less in numbers, at least of those studied.
It was originally believed that CRISPR systems in bacteria only targeted viral DNA and that any RNA specific phages would be free to attack bacteria….
But that isn’t entirely true for all bacteria. Last year, a new CRISPR system named C2c2 was found in the bacteria Leptotrichia shahii that does specifically target viral RNA, showing that there are indeed some bacteria that develop those sorts of defenses when they need it. And this was an important find, as being able to target RNA for editing as well opens up even more options for the future.
There are five primary types of Cas systems, running from the roman numerals of I to V (The RNA-based C2c2 system mentioned before might actually count as a new type VI), though they are largely classed into two functional groups. Types I, III, and IV are grouped together because they all make up what are called multiprotein effector complexes. What are those?
The GLP aggregated and excerpted this blog/article to reflect the diversity of news, opinion, and analysis. Read full, original post: CRISPR: An In-Depth Primer On All Its Varieties
For more background on the Genetic Literacy Project, read GLP on Wikipedia