"SMEAR" BUT NO BANDS WHEN DOING "LONG" PCR USING KLENTAQ1 WITH PFU

[Christian Beltinger]

RE:  "SMEAR" BUT NO BANDS WHEN DOING "LONG" PCR USING KLENTAQ1 WITH PFU	 

		I am trying to PCR-amplify a stetch of genomic DNA   cloned into a
cosmid.  I do not know the size of the genomic DNA, since its genomic
structure is unknown.  (Only the sequence of the cDNA is known, from which
I constructed 33mer primers for PCR).  I guess that the size of the gene is
about 12kb.  I used a 16:1 mixture of Klentaq1 (from AB Peptides, St.
Louis) and PFU DNA polymerase (Stratagene) in PC2 reaction buffer (AB
Peptides). I used 10pmol of each primer, 10 ng of cosmid and 1.2 ul of the
Klentaq1/PFU mixture.  The reaction volume was 50ul.  I used the Omnigene
Hybaid cycler with no initial denaturing step and then cycled with 2s at 95
degrees and annealing/extension temperature of 68-72 degrees for 24 minutes
for 24 cycles (according to Barnes' paper in PNAS in March '94).

		Consistently, I get these surprising results when running out 25-50 ul on
an 0.8% agarose gel:  Instead of discrete bands there is an intense
homogenous smear from the well down to the dye front , even in samples
without DNA template!

	Does anyone have an explanation for this phenomenon and a suggestion how
to avoid it?

Thanks a lot!