Download Full Text (1.9 MB)


Bacteria and the viruses that infect them have been at war from the beginnings of life until today. Due to selective pressure from viral infection, bacteria have evolved various biological defense systems, including CRISPR-Cas systems that use a genetic memory of previous viral encounters to protect against future invasions. However, recently it has been shown that viruses have evolved counter-strategies to evade CRISPR systems. Virally encoded proteins called anti-CRISPRs use a variety of mechanisms to block the activity of CRISPR immune systems in order to infect bacterial cells. The Jackson lab at USU recently showed that a Type IV-A CRISPR-Cas system native to the bacteria Pseudomonas aeruginosa is a bonafide defense system, but an anti-Type IV CRISPR mechanism has yet to be described. We identified 51 genes that we hypothesize to have anti-Type IV CRISPR activity. Using a colony PCR assay plasmid curing assay we screened each of the putative anti-CRISPR genes for activities that block Type IV CRISPR system targeting. Several of the putative anti Type IV-CRISPR genes have protected target sequences in our assay indicating Type IV anti-CRISPR activity. These identified genes will be expressed and purified in an attempt to better understand the mechanisms of Type IV CRISPR system inhibition.

Publication Date



Logan, UT


CRISPR, immune system, bacteria, viruses



Discovering Virally Encoded Proteins That Block Type IV CRISPR Immune Systems

Included in

Biochemistry Commons