Plasmid changes after transformation - (Jul/14/2005 )
These days, i am being in a trouble that my plasmids changed during the transformation.
First, i run the plasmid on the gel, and it is ok, just the size it is. then, i transform DH5@ with it, and after extract the plasmid from the transformed strains, it becomes 6 bands, which appears to be two different plasmids. and when i digest it, it comes two linar bands. So i think it is contaminated with other plasmid, and reselected the strains to find that all the strains are having the same plasmids----two different plasmids.
So i think something has happened to my plasmid. what is it? How can i get my target plasmid again?
I am looking forward for your comments.
you checked your DH5a's for having a plasmid before you transform them?
Maybe this is a good approach. i will check that. Thanks!