neomycin-G418 confusion

Bernard P. Murray, PhD bpmurray*STUFFER* at
Thu Oct 29 15:12:23 EST 1998

In article <717ico$n04$1 at>,
wolfgang.schechinger at wrote:

> Hello Martin, 
> The story about Neomycin and G418 is this: 
> 1. The NeoR gene is coding for neomycin phosphotransferase
> 2. Neomycin binds to ribosomes in certain Prokaryotes
> 3. G418 binds ... Eukaryotes
> 4. Neomycin phostransferase phosphorylates both G418 and Neomycin and 
> renders them inactive.
> 5. G418 is only effectice in Eukaryotes

I don't think that this is true.  I believe that G418 does
kill bacteria but it is so expensive that it is not routinely
used for selection in prokaryotes.  On the positive side
your cultures of eukaryotic cells in G418 almost never become
contaminated (unless you are *really* messy - who, me?).

> 6. Neomycin ... Prokaryotes. 
> This all is written down nowhere. It seems to be 
> common sense <GG>.  
> 7. Maybe those guys who are writing the catalogues are reading this 
> message here and will include these hints in every catalogue.
> Wolfgang 

You may wish to add that kanamycin is routinely substituted
for neomycin (for selection in prokaryotes) as this is also
a substrate for the product of the neoR gene.

Also G418 = geneticin (not to be confused with gentamycin)

In yeast vectors you will often see neoR as the kanMX marker
(but you have to use G418 for selection).

Probably the archetypal mammalian vector is pSV2neo which
has neo under the control of the SV40 promoter.  However
this was made with most of the original (?Tn5) cassette
and contains a prokaryotic promoter and so confers resistance
to kanamycin in bacteria.  Some vectors (eg. Promega's pCI-neo)
no longer have this promoter and so transformed bacteria are
kanamycin sensitive.
     Always room for more confusion....
Bernard P. Murray, PhD
Dept. Cell. Mol. Pharmacol., UCSF, San Francisco, USA

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