OD and IPTG concentration

Duncan Clark junk at
Sat Dec 22 06:38:56 EST 2001

In message 
<Pine.SOL.4.33.0112211041150.15143-100000 at mcmail.cis.mcmaster.ca>, Kyle 
Legate <legatek at mcmail.cis.mcmaster.ca> writes on the Fri, 21 Dec 2001
>Please share some methods to maintain vectors without antibiotic. I always
>thought that if the bug has no use for the resistance marker, it would
>dump the plasmid, no exceptions.

The first one that springs to mind is the hok/sok system (parB ?) in R1 
type plasmids but can be put into others.  Have a look on Pubmed for it 
and you should find quite a few references including one in an old 
Nature Biotechnology with some interesting stabilisation facts for 
various plasmid origins i.e. pACY vectors with p15a replicon get lost 
quite quickly without selection. Put in the small hok/sok system (few 
hundred bp) and the stability is improved a thousand fold i.e. it is 
then very difficult to lose.

Actually this may of value to those people using T7 expression vectors 
with lethality problems. Putting in hok/sok should offer a better 
selection than ampicillin with the caveat that growth will be slow (due 
to toxicity of protein product) and it may actually force selection for 
deletion/rearrangment variants :-(

Still may be worth a try.

To all our many readers, have a good Xmas and New Year :-)

The problem with being on the cutting edge is that you occasionally get
sliced from time to time....

Duncan Clark
GeneSys Ltd.

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