The CRISPR system is divided into two classes (I and II), in which class II is the basis for the famous CRISPR-Cas9 system used in several experiments published today. This class, however, is not abundant in nature, covering only 10 percent of the system in sequenced bacteria and archaea. Class I is the more abundant type of the system, but the mechanism of enzyme recruitment during immunity is less studied.

Scientist MaryClare Rollins of Montana State University and colleagues used cryo-electron microscopy to determine the mechanism of Cas enzyme recruitment in the CRISPR system in bacteria. Results showed that a 180 degree shift of a part of the system is involved when the system is bound to the double-stranded DNA. They also found that the complex is mimicked by an "anti-CRISPR," indicating that the class I system may be involved in the evolution of these anti-CRISPRs.

For details, read the article in bioRxiv.