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Six strains of E. coli distantly related to E. coli K-12 have been observed to overproduce certain recombinant proteins. These strains, now available as TOPP competent cells (1-6) , provide a rapid alternative for improving protein expression without subcloning

Our lab has the following TOPP Strains:

1. TOPP 1

   3x10(4) transformants per ug of DNA

2. TOPP 2

   3x10(4) transformants per ug of DNA

3. TOPP 3

   1x10(5) transformants per ug of DNA

4. TOPP 4

   400 colonies per ug of DNA

5. TOPP 5

   1.1x10(5) transformants per ug of DNA.

   Too much DNA seems to inhibit transformation and in these cells 1/1000 dilution seems to be the peak.

   Note:These cells are sensitive to loss of F'-- need to be grown in presence of tetracycline or chlorannnphenicol at all times!

6. TOPP 6

   1.1x10(5) transformants per ug of DNA