Question

We know that two things must be recognized by Cas9 before it will perform cleavage: (1) the correct PAM sequence, and (2) adequate base pairing between the spacer sequence of the RNA and the candidate DNA target. We also know that PAM recognition happens first. Does this make sense? In other words, if you were designing an enzyme that had to do these two tasks (in the same way that Cas9 does them), would you choose to test for PAM recognition before the check for a sequence match between RNA and DNA? Why or why not?

Answer 1

Answers CRISPR/Cos systems are used by bacterial cells to protect itself from viscal genomes. CRISPR'S ( clustered Regularly Inperspaced shoot palindromic repeats) consist highing conserved ghost repeated sequences separofed by spacer Sequences and present in bacteria. Spacers' are derived from invading virus and stored in CRISPR aproy momosy and filized by bacteria is fufurre if same visus attacks again. If same visus affacts again, sequences that are recognized by bacteria are called os profoecepceas but these are some as the spacers in bacterial DNA. PAM (Poo fospacer Adjacent motif , a to 6 nucleotide sequences present only in uinol genome adjacent to protospacer helps yo distinguish between virrey and bacterial DNA and prevent bacterial DNA to breakdoon by casg protein. It also reduces time to search the desirable DNA sequence · If PAM recognition is not happens first then bacferia may cuf its own DNA, hence it does make sense to recognize pam first before the sequence mateh.