high melting temperature in site directed mutagenesis - (Mar/11/2008 )

Hello
can anyone explain me why the primers for the site directed mutagenesis require high melting temperature.
I cannot figure it out.
thank u.

Its a PCR so one has the high temp. for denaturation.

Site-directed mutagenesis primers are usually designed with the mutation in the middle of the primer. This region does not anneal to the template. This creates a situation where each half of the primer needs to be treated like a separate primer, particularly if you are using a splice-overlap PCR to create the mutation. The first PCR depends on the annealing of one half of the primer and the final joining PCR depends on the annealing of the other half of the primer, so both halves need a sufficient Tm to anneal to the template in the respective PCRs, which is usually why they are so long and the Tm of the whole primer is so high.

Seeya, Rob