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Making Competent Cells - DH5A vs JM109 or anyother (Feb/07/2007 )

Hello there,
My lab is trying to make competent cells and wondering which cells to use of: DH5alpha vs JM109. Could anyone tell me the advantage n' disadvantage of both of them. Is one of them better than other or it depends on which vector we using?

Thanking You,
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I havent used the JM109 but I know DH5alpha to be very good. I know many labs use DH5alpha.


I am using both of them. JM109 is also very good. I have used JM109 instead of DH5alpha although DH5alpha is the recommended one and I have faced no problems. I don't know actually whether there are any crucial differences between those two or not.


I use DH5A too. So far not many problem. JM109 has additional strain. The end- strain.... You need an additional step for plasmid prep for that.


JM109 and DH5alpha are usually equivalent, but there are a few exceptions. The Promega website mentions a few plasmids that are not stable in JM109, and there are probably more.

"We maintain most of our plasmids in JM109 cells, but there is no need to use only JM109. Most of our plasmids should grow in standard E. coli strains such as DH5alpha™ or XL-1 Blue. Exceptions to this include our pALTER-Ex1 and pALTER-Ex2 Vectors, which grow very slowly in DH5alpha™, and the discontinued pCAT line of vectors, which are not stable in JM109 cells. If you have the discontinued pCAT Vectors and wish to make more, use HB101 bacteria to propagate the plasmids." - Promega website


DH10B, DH5alpha, XL-1 Blue, and JM109 are all good.

For 99.99999% of applications, they are equivalent.