Q: PCR cloning

[Jinling Xie]

Hi, there,

     I've been cloning small size PCR products which are 150bp and
115bp with Bam HI and EcoR I ends. I've done many times with the 
molar ratio (V:I) in 1:1 and 1:3 into pBluescript SK+. I purifed
the plasmid and PCR products from agarose gel with QIAEX II after
digestion. It seems to be simple cloning. However, I couldn't get
positive fragment until now. I don't understand what's going on
except to doubt the PCR porducts can't be cut or SK is not easy
to be cut with BamHI and EcoR I at the same time. Anybody happens 
to have the similar experiences on this, would you please share 
with me? Your help would be highly appreciated.

Jinling