Long PCR primers

[AShaw5, by way of "David L. Haviland, Ph.D." <dhavilan at imm2.imm.uth.tmc.edu>]

>I use PCR primers like that all the time.  However, I'm worried about the
>12 bp priming region.  For my tastes, that is too short.  I generally like
>18-21 minimum.
>Andrey Shaw

Greetings:

I second Andrey Shaw's suggestion.  I have personally PCRed upwards of 5 kb but
the only way I was able to do this was in using 35-40 mers in which no 
restriction sites were engineered within either oligo.  "In my hands", long PCRs
required higher annealing temps and as a result, I 'd design my oligos with
no less
than a 65-68'C annealing temp and if that meant that it was a 30-40mer to do
it, 
so be it...

Best of luck,
David