FAQ: What if my primer extension reaction yields no product or a smear?
* Optimize annealing and extension temperatures
* Optimize Mg2+ level
* Optimize amount of polymerase
* Purify DNA template by phenol/chloroform extraction and alcohol precipitation
* Avoid high salt carry-over into primer extension reaction
* Make sure dNTP solution has not undergone hydrolysis - try fresh dNTPs
* Cosolvents such as 100 mg/ml BSA, 1-10% formamide or 1-10% DMSO may help with some primer: templates