DH5a, Xgal and IPTG

Karen Nel karen at scientia.up.ac.za
Fri May 9 17:26:47 EST 1997

I saw a posting about not having to use IPTG along with Xgal for selection of 
transformed DH5a cells.  I have transformed DH5a cells with a pBS plasmid and 
plated them on to LB agar with Xgal and with and without IPTG.  On the plates 
with IPTG I got only white colonies and on the plate with Xgal I got blue and 
white colonies.  Isn't this the opposite of what one would expect?  Could 
someone perhaps explain the mechnaism of blue-white selection with Xgal?

Thank you in advance

Karen Nel
Karen Nel                                             karen at scientia.up.ac.za
Department of Biochemistry
University of Pretoria

More information about the Methods mailing list