cold-labile plasmid

[Elizabeth K Winters]

I am working with a plasmid which behaves abnormally at cool 
temperatures.  This is a 2.96 kb pBluescript vector containing a 
highly-repetitive 1.6 kb cDNA insert.  I have used the vector to 
transform E. coli strains XL1-Blue and DH5-alpha, by heat shock and 
electroporation.
When the bacteria are kept at room temperature or warmer, I can digest out
the 1.6 kb fragment as usual.  However, when the bacteria containing the 
plasmid are cooled to 4 degrees Centigrade or frozen (including in 
glycerol stock), the plasmid digestion results in only a fragment of the 
original insert.
Has anyone ever heard of a plasmid behaving in such a cold-labile way?  
Do you ahve any ideas about what is happening?  We suspect the fact that 
the insert is highly repetitive is important.
I have more information if anyone is interested.  I appreciate any input 
that I may receive.  Thank you.

Beth Winters
ekw2 at iastate.edu
-- 

Beth Winters
ekw2 at iastate.edu

"We drift down time, clutching at straws; but what good's a brick to a 
drowning man?"  (Tom Stoppard)