XGAL & IPTG -- how low can you go?

Chris Boyd chrisb at hgu.mrc.ac.uk
Mon Feb 17 04:59:47 EST 1997

Ann L. Williams (awilliams at biochem.okstate.edu) wrote:
: We have good luck with applying the IPTG & X-Gal to the surface only 
: of the plates.  As always TIME=$.  I mix small amounts of my two 
: stocks and spread 100ul of this stock on the plates circa half an hour 
: before I plate my cells (spread or streak).  The stocks we use:
:    2%   X-Gal (in pmsf)
:   100mM IPTG

The danger of spreading Xgal on top rather than mixing it in with
molten agar is that it may well end up having a non-uniform
distribution in the plate.  In zones where there's less of it, even
non-recombinant colonies will grow up white, so you could waste more
time and money screening false positives.  My advice: put Xgal in the
molten agar every time.  If you want to save money, omit the IPTG
altogether. It makes little difference with high copy number vectors
such as pUC, BlueScribe etc.

Best wishes,
Chris Boyd                       | from, | MRC Human Genetics Unit
chrisb at hgu.mrc.ac.uk             |  not  |  Western General Hospital
http://www.hgu.mrc.ac.uk/~chrisb |   for |   Edinburgh EH4 2XU, SCOTLAND

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