how long a primer should I use? - (Apr/10/2005 )

hi, I am cloning from cDNA but failed. As I go through literature, it occured to me that people have used some pretty long primers for this kind of work, I just wonder how long should the primer be to be able to get products? Though other factors may also affect the result of PCR, I want to make sure that my primers, in the first place, is not too short for it.

thansk!!

Hi,

What is the length of your existing primers and how big is your product? The problem may not lie in primer length. Primers around 18-25 should work for most PCRs.