gentic questions

Michael Cooley szcooley at
Fri Mar 10 18:59:18 EST 1995

Oscar Barriuso (barriuso at wrote:
: Can someone please help me answer these questions.

: When cloning foreign DNA, usually a bacteria host that has a mutation in 
: its restriction enzyme gene but a normal modification enzyme gene (r-m+)
: is used.  WHY ?

Originally it was desirable to have the DNA modified if you ten wanted to 
move the plasmid into a new strain which was wild-type for the 
restriction system. It is not as important now because most lab E. coli's 
are restriction minus.

: It is not possible to clone some gene on high copy number plasmids.  Suggest a
: a biological reason why this might be true.

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