Question

Shown below is the start of a coding region within the first exon of a gene. 5'-GCTCTTAGATATTCCACGACACAGCATGTCAAGAGAAGTACAGTAATGACGGACTAGTA-3' 3'-CGAGAATCTATAAGGTGCTGTGTCGTACAGTTCTCTTCATGTCATTACTGCCTGATCAT-5' What is the PAM sequence of the bottom strand of DNA?

Answer 1

3'-GGT-5'

Step-by-step explanation:

• Protospacer adjacent motif or PAM is an important part of the CRISPR/Cas 9 gene editing system.
• CRISPR/Cas 9 is a popular gene editing tool that uses an RNA guided endonuclease that cuts DNA at precise target points.
• As shown in the picture, the CRISPR/Cas9 system consists of the following parts:

1. Cas9 endonuclease
2. Guide RNA complementary to the target sequence.
3. PAM sequence - a 3 nucleotide sequence on the guide RNA that helps the Cas9 in recognizing and binding to the target DNA.

• PAM sequences are located 3-6 nucleotides downstream of the target DNA.
• Every endonuclease recognizes a different PAM sequence. However, the most commonly used Cas9 from Streptococcus pyogenes recognizes the sequence 5' NGG 3'. The "N" represents any nucleotide.