I am pretty new in the field of protein purification. Normally I use AHT (anhydrotetracycline) to induce E coli BLR strain and p-ask-IBA3 as vector. Is there any difference between using BLR and BLR (DE3) for protein expression? Or maybe are they the same?
BLR(DE3) has the DE3 lambda prophage, which carries the gene for T7 RNA polymerase. Thus, you can use BLR(DE3) for expression of genes under the control of a T7 promoter, but not BLR. In the case of "normal" promoters (sigma factor 70-dependent) such as yours, it does not make a difference and, for some applications, it may even be preferable to use plain BLR.
As an aside, in colloquial lab jargon it is common to ommit the DE3 part, so if a colleague is referring to "BL21" or "BLR" chances are they are actually referring to their DE3 derivatives.
Hope it helps!
Hi there,
The only difference is that DE3 lysogene (insertion of phage DNA into the bacterial genome) allows IPTG inducible expression of T7 RNA polymerase in BLR (DE3) which is absolutely required for T7 promoter driven transcription (in summary DE3 is necessary when using pET vector). So it's not the case for you : BLR strain is enough for pASK driven expression of protein, BLR(DE3) would be a waste...
from the IBA website:
..The following E. coli strains have already been used successfully for Tet expression with our pASK-IBA vectors: JM83, WK6, B, BL21, MG1655, W3110, BL21(DE3), BLR(DE3), XL1-Blue, BL21-CodonPlusTM-RIL..
I think that the genomic background does not matter here, these plasmids don't
need T7 RNA polymerase.
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