Well, Cas9 recognizes a specific Protospacer Adjacent Motif or PAM for short which is a conserved 2-5 base pair sequence located near the crRNA complementary sequence.

Cas9很快会识别特定的" 原间隔序列邻近基序" （简称PAM）；PAM是病毒位于crRNA互补序列附近的2-5对保守的碱基序列。