I'm designing a set of primers and reading about the principles of primer design one of which is:
GC Clamp: The presence of G or C bases within the last five bases from the 3' end of primers (GC clamp) helps promote specific binding at the 3' end due to the stronger bonding of G and C bases. More than 3 G's or C's should be avoided in the last 5 bases at the 3' end of the primer.
From here.
My question is how essential is it to have a GC clamp?