Yes. For all plasmids containing the lambda phage promoter (P70a, P70b, P70c, P70d) it is extremely crucial to use E. coli KL740 as the transformation strain. When cultivated below 30°C, this strain over-expresses the lambda phage repressor protein Cl857 that represses P70 promoters, thus ensuring high transformation efficiency and plasmid stability. KL740 can be purchased from E. coli Genetic Stock Center (Yale) [CGSC#: 4382] or from Daicel Arbor. For all other plasmids, a standard laboratory E. coli cloning strain like JM109 or DH5alpha is sufficient.