low Tm primer PCR

Zhengyu Sha zsha at iastate.edu
Sun Dec 13 19:42:25 EST 1992

I have problem with a low Tm(46.8) 18mer primer in my PCR. My setting is:
95C 15sec.  41C 1.5 min. 72C 2.5 min. The other primer(18bp) has a 55.5 Tm. 
So the two primers are quite deferent in their Tm.( I know I should use two
two primer which have the same Tm above 55C, but I just want to use the primers which I synthesized for sequencing). I have no problem when i use a primer(Tm 48.6) with annealing Tm=43C in my PCR (the other primer is that 55.5 Tm primer). My question is since the annealing Tm is quite low do I have to low my extension Tm( I tried 70C, no help)?
Thanks in advance!  
 $       Zhengyu Sha                  |    2188 Molecular Biology Building    $
 $   Phone No. (515)294-4210          |    ISU, Ames,Iowa 50011               $
 $=I think what I said is the official opinion of ISU, but no one believe it.=$

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