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e coli strain selection for protein expression - (Jun/23/2010 )

Hello, in our lab we have BL21 pRARE chemically competent cells which I have been told are used in protein expression experiments. Does this mean the pRARE plasmid is already transformed into the strain? If so, how can I then transform in my plasmid expressing my protein? The pRARE gives chloramphenicol resistance while my plasmid gives kanamycin resistance. Should I grow the cells on plates with both or just kanamycin?

Thank you


pRARE has a p15a origin of replication and is therefore compatible with common expression vectors like the pET family who have a ColE1-like origin of replication you don't have to worry!

I would use both antibiotics to prevent plasmid loss of both plasmids!

Good luck for your expression experiments!



You'll need both antibiotics. You may need chlor in the recovery SOC medium, tho'.

When all else fails, I'd just check with the website...