low plasmid yields in dh5alpha

[Murata Takehide]

Dear Ed, 
Reduce the cultivation period.  During long period, E. coli may lose plasmid but get anti-antibiotics secreted in media and E. coli can be alive. 
 
Take
http://www.brc.riken.jp/lab/dna/
 
> Hi.  We've been going through our old plasmids and makingfresh stocks.  We've found a few that we're not able tominiprep and get reasonable concentrations (<50ng/ul).We're using Qiagen miniprep kits and invitrogen dh5alphaand have had much success purifying>One thought was that the plasmids might be producing aproduct that is toxic to dh5alpha, and maybe they'd dobetter in another strain. Has anyone had a similar problemthat was resolved by growing the plasmid in another strain?>I'm thinking XL1-blue might help because it retains thelac repressor, and that might help stop any backgroundexpression from the lac promoter.  Any other ideas wouldbe appreciated.  Thanks>-Ed
 
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