Induction strength : IPTG vs lactose - which one is stronger? (Mar/08/2011 )

If I use the same concentration of lactose and IPTG for induction under lac promoter, would they give the same amount of protein expression?

hola, difficult and easy question: The strengh of IPTG depends of the numbers of occuped promoters for it = cell number x copies of plasmid, Usually if you add and excess of IPTG growth stops and cell only works to produce protein(OD constant ) and after 3-4 hours bacteria can have lysis. Lactose induces and serves as substrate, so bacteria continue growing and produce protein and is less probable the lysis. Moreover, excess of IPTG could lead to insoluble aggregates and with lactose the regulation of lactose permease Lac Y regules the entry of lactose of a more controlated way. In my case I prefer always lactose. I hope this could help you. Buena suerte

Thanks, that's really informative!