Did you attempt PCR using *THIS* plasmid as a circular template? If you already have, then you obviously need to try linearizing it first. You could probably use HindIII. Remember to purify the digest (with the PCR clean up kit?) before attempting PCR on it. You may want to run it on a gel after the digest to make sure that you have 2 fragments of about the right size: ~1800 pb and ~ 4900bp plus whatever size the insert is. While circular DNA seems to be less efficiently amplified than linear DNA, it should still work--see http://amrita.vlab.c...6&sim=321&cnt=1
Keep in mind that things occasionally get mislabeled in the lab, so you may not have the plasmid you think you have. Doing a few other restriction digests and running them out on a get could be very informative. Here is a site with the restriction map for your plasmid: http://www.snapgene....troX-Tight-Pur/
Finally, you need to realize that PCR may not be extremely high fidelity, depending on the kit you use. To avoid accidentally adding in a mutation, you will need to sequence the PCR product you get and the new plasmid into which you clone it.
You could also confirm that you have the correct plasmid by finding some primers that should work for sequencing and send it off. Assuming you get something back, you could then blast it against the NCBI data base.