Q : E. coli instability

[Elizabeth Lawrence]

Hi fellow cloners,

I am having problems with JM109 E. coli maintaining my plasmid.  The 
plasmid is a vector plus a viral genome from which I have deleted about 
800bp.  I have gotten colonies from electroporation of these bacteria and 
up to this point I know I have the right DNA fragment-from gel analysis.  
However, after culturing and maxi-prepping it appears that only the 
vector was maintained and the entire viral genome was "kicked out".  
Please let me know if you have a clue as to why this may be occurring.

Thanks in advance, Liz  eclawrence at ucdavis.edu