Final answer:
The subject of this question is Biology, specifically the endonuclease involved in the CRISPR system. The endonuclease mediates cutting of DNA at a site complementary to a 20-nucleotide sequence on the 5' end of the guide RNA (gRNA).
Step-by-step explanation:
The subject of this question is Biology. Specifically, it is related to the CRISPR system and the endonuclease involved in it.
The endonuclease referred to in the question is a type V restriction enzyme in the CRISPR system. It mediates cutting of DNA at a site that is complementary to a 20-nucleotide sequence on the 5' end of the guide RNA (gRNA).
For example, when an invading phage DNA is targeted by the gRNA, the endonuclease recognizes the complementary region and creates a double-stranded break in the DNA at that site.