Overview
The BL21 cells are fairly fussy in that, unlike other E. coli strains, their plasmids become unstable if the cells are stored in glycerol concentrations greater than 10%. For this reason, the cells should be stored in 8% glycerol and frozen quickly in liquid nitrogen.
Details
Details of this protocol, Preparation Of Glycerol Stocks, Thawing Of Stocks, are located on a web site other than Biocompare Protocols.