need BL21A(DE3) strain of E. coli

Ashok Aiyar aiyar at
Sun Feb 8 21:34:53 EST 1998

On 8 Feb 1998 20:03:56 -0500,
Daniel Gonzalez (meton at wrote:
>dalmiabk at (bipin k. dalmia) writes:
>>i need the e.coli strain BL21A(DE3) for expression of a foreign
>>protein. this strain is a derivative of BL21(DE3) with the addtional
>>mutation dam-13::Tn9.
>You can obtain that strain as well as HMS174(DE3) from Novagen

Novagen doesn't appear to sell or provide BL21A(DE3) - at least it
isn't on their website or in their catalog.  As Bipin mentioned,
BL21A(DE3) is a dam(-) BL21 derivative made by Sanford Lacks and
his co-workers to express the endonuclease DpnI in.  DpnI cleaves
methylated and hemi-methylated DNAs, rendering expression in dam(+)
strains of E. coli near impossible.

I know BL21A(DE3) can be obtained directly from Dr. Lacks - don't
know if are any "commercial" sources.

Ashok Aiyar, Ph.D.
McArdle Laboratory for Cancer Research
aiyar at

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