Induction of LacZ without IPTG - (Apr/23/2007 )

Hi there,

Here is my story... I have been using SURE cells for transformation. I use Xgal and get blue and white colonies. The thing is that SURE cells express the LacZ repressor, i.e. they have LacIq, so we do not understand how the LacZ gene is being induced without addinn IPTG.
Thanks a lot for your advice!!!!

LacIq is only to control the strong polymerase and to avoid leaky expression.
Is your protocol without adding IPTG? I think there are other inducer like antibiotics to substitute IPTG.

lactose in your media?
The lactose could be leaking from your yeast extract. At moderate aeration you only need 0.001%w/v to see induction. 0.05% for to see induction at high aeration. And 0.2% will fully induce your protein regardless of aeration conditions.

I would suggest adding glucose, 0.05%w/v (final concentration) glucose to inhibit this case of "auto induction".