PCRing B-gal transgene?

[Jennifer Schmitt]

Does anyone have experience using PCR to detect the presence of a
B-galactosidase transgene from mouse tail genomic DNA?

I have been trying to do this but keep seeing a band of varying intensity at
the same position as my target band even in known non-transgenic DNA!

I am pretty certain this is not contamination:  H2O control lane is negative,
band is present in DNA even borrowed from another lab that has never been near
a B-gal plasmid, etc.

I know there is endogenous B-gal activity in some mouse organs but I thought
this was not from an endogenous B-gal gene.  Any idea what I am seeing?

Also the transgene is based on the vector pNASSB from Clontech, has anyone
successfully made primers to detect this construct as a transgene?

Thanks, Jennifer