Why do a bacterium need CRISPR system?
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4 weeks ago
Farhat • 0

I'm learning about CRISPR at my college.
I understand that when viral DNA is inserted into a bacterial cell, the Cas1-Cas2 proteins identify the PAM site in the viral DNA and then cut the protospacer from the viral DNA to make it a spacer in the CRISPR array for the adaptive immunity of the bacteria. I'm confused about why they need the CRISPR system if the Cas1-Cas2 cuts the protospacer, and at that time only the viral DNA gets inactivated.

CRISPR Genetics • 628 views
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4 weeks ago
Mark ★ 1.6k

Cas1-Cas2 is part of CRISPR.

it's not a separate system. the C in Cas is CRISPR.

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Then what is the need for Cas9 in bacteria?

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It infers adaptive immunity for the bacterium against invading foreign DNA, think phage/viruses.

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But cas1-cas2 is also doing the same thing right?

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Those are different types of nucleases. They form part of the CRISPR system. See: https://en.wikipedia.org/wiki/Cas12a

Cas12a is distinguished from Cas9 by a its single RuvC endonuclease active site, its 5' protospacer adjacent motif preference, and for creating sticky rather than blunt ends at the cut site.

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Thanks. Now I understood it

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