Digestion question - (Sep/07/2007 )

I am digesting a vector prior to performing a ligation and have got some unexpected bands.

I need to digest with XhoI and NotI so I did the double digest and both as single digests to check they were working. I got the expected 10k band with XhoI but with NotI there was an additional 5-6kbp band and the 10kbp band. The total size of the plasmid is 10kbp so where has this band come from? NotI was expected to cut once.

The double digest had the 10kbp band and also a very faint band at 5-6kbp, I have cut out and purified the 10kbp band, will this be correctly cut with XhoI and NotI?

I am getting very confused here! Thanks for any help

Is it possible that your NotI stock is contaminated with another restriction enzyme? If I had this result, I would buy another tube of NotI and try again.