BL21 vs. DH5a

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BL21 vs. DH5a

Postby Yoon » Apr 23 2003 2:09 am

Hi,

What are the differences of expreesing GST-fused protein in BL21 and DH5 alpha?
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Postby Replicon » Apr 23 2003 4:15 am

Hi

DH5 alpha are a suitable strain for plasmid maintenance and growth but, unmodified, they are not suitable for expressing recombinant proteins. It is more than likely that transcription of your GST fusion protein is controlled by T7 polymerase, of which DH5 alpha do not encode (unless you have transformed them with a suitable plasmid). BL21 (at least DE3 lysogens) encode the T7 polymerase, which is inducible with IPTG, allowing transcription of your recombinant protein.

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Postby Yoon » Apr 23 2003 4:41 am

Thank you for the reply, Cherry.

The vector where my protein is in is pGEX4T3, which is controlled by tac promoter. So that has nothing to do with T7 RNA polymerase.

Anyway... one more thing.
Then, why is it that some use DH5 alpha as a host strain for GST-protein expression?
I've seen it several times in the paper.
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Postby Replicon » Apr 24 2003 5:25 am

Hi

Without seeing the paper I can only really guess. It may be that the vector used encoded functions that allowed expression of recombinant proteins in this strain or the strain may have been modified in some way to also allow expression. Alternatively a non-standard promoter may have been used. The DH5alpha genotype may be more suitable for expression of this/these particular proteins also?

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Re: BL21 vs. DH5a

Postby Nageena » Oct 23 2010 10:02 am

hi

could you please tell me about DH5 alpha as recombinant deficient starin. i used vector which has full lacZ gene. i want to express that gene in suitable host. i find dh5nalpha best due to deficiency of recA gene, so no recombination would occur with my lacZ gene and mutated lacZ of dh5alpha. can anyone suggest anyother suitable host as dh5alpha is not protease deficient, so the quantity of my protein may be less in this strain. secondly my vector does not have lacI repressor sequence, so do i need to provide lactose in medium for stability purpose of b galactosidase irrespective of induction purpose.????????

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