What is the Difference Between BL21 and BL21 DE3?

The main difference between BL21 and BL21 DE3 lies in the presence of the T7 RNA polymerase gene. BL21 is an E. coli B strain that does not carry the gene for T7 RNA polymerase, while BL21 DE3 is an E. coli B strain that carries the gene for T7 RNA polymerase.

BL21 DE3 is a derivative of BL21, which has the T7 RNA polymerase gene under the control of the lacUV5 promoter. This arrangement is on a phage genome called DE3, which is inserted into the chromosome of BL21 to make BL21(DE3). The presence of the T7 RNA polymerase gene in BL21 DE3 allows for expression from a T7 or T7-lac promoter or promoters recognized by the T7 RNA polymerase, such as lac, tac, trc, ParaBAD, PrhaBAD, and the T5 promoter. In contrast, BL21 does not carry the gene for T7 RNA polymerase and is only suitable for expression from promoters like lac, tac, trc, ParaBAD, PrhaBAD, and T5.

In summary, the key differences between BL21 and BL21 DE3 are:

• BL21 does not carry the gene for T7 RNA polymerase, while BL21 DE3 carries the gene for T7 RNA polymerase.
• BL21 DE3 is suitable for expression from a wider range of promoters, including T7 or T7-lac promoters, while BL21 is limited to promoters like lac, tac, trc, ParaBAD, PrhaBAD, and T5.

Comparative Table: BL21 vs BL21 DE3

The main difference between BL21 and BL21 DE3 is the presence of the gene for T7 RNA polymerase in BL21 DE3. Here is a table summarizing the differences between the two strains:

Both BL21 and BL21 DE3 strains are competent E. coli cells extensively used for recombinant protein expression and have an identical genetic background. The presence of the T7 RNA polymerase in BL21 DE3 allows it to be used with a wider range of promoters, including the T7 promoter.