CRISPR

Question 1

How does the bacterial immune system acquire new spacers from invading phages into the CRISPR array?

Answer 1

Novel spacer acquisition is done by Cas1 and Cas2 in both Type 1 and 2 systems. Cas1 and Cas2 proteins recognize the PAM sequence and cleave the protospacer downstream of the PAM, and incorporates it as a novel spacer in the chromosomal CRISPR array.