=JM83 hsdR

= RR1 del(malB) del(lac)U169 pro+ fhuA

The malE gene is included in the malB   deletion, so this strain does not make any MBP from the chromosome.  It does not have the lacZdelM15 allele, so it cannot be used for a-complementation (no blue-to-white screen on Xgal).  This strain can be transformed with high efficiency, similar to RR1 and HB101.

= RR1 lon del(malB) del(lac)U169 pro+ fhuA

The malE gene is included in the malB   deletion, so this strain does not make any MBP from the chromosome. This strain can be transformed with fairly high efficiency, about 10x down from RR1 and HB101

CAG626 is ECOk r+m+, so your plasmid has to be modified (i.e., come from an m+ strain such as TB1, JM83, JM107, etc.) in order to get transformants; the transformation frequency is about 100x down from other common strains used for recombinant DNA work, so it helps to use electroporation. (from C. Gross; Baker et al., 1984, PNAS 81, 6779-83)

rpoHam = htpRam, codes for the heat-shock sigma factor; this strain has a temperature-sensitive amber supressor (supCts), and should be maintained at 30°C. When you induce your expression system (e.g. when you add IPTG), shift the cells to 37o or 42°. CAG597 is ECOk r+m+, so your plasmid has to be modified (i.e., come from an m+ strain such as TB1, JM83, JM107, etc.) in order to get transformants; the transformation frequency is about 100x down from other common strains used for recombinant DNA work, so it helps to use electroporation. (from C. Gross; Baker et al., 1984, PNAS 81, 6779-83)

rpoHam =htpRam, codes for the heat-shock sigma factor; this strain has a temperature-sensitive amber supressor (supCts), and should be maintained at 30°C.   When you induce your expression system (e.g. when you add IPTG), shift the cells to 37° or 42°C. CAG629 is ECOk r+m+, so your plasmid has to be modified (i.e., come from an m+ strain such as TB1, JM83, JM107, etc.) in order to get transformants; the transformation frequency is about 100x down from other common strains used for recombinant DNA work, so it helps to use electroporation. (from C. Gross; Baker et al., 1984, PNAS 81, 6779-83)

thr::Tn10 dnaJ259 leu fhuA2 lacZ90(oc) lacY glnV44 thi

This strain, an F- derivative of CAG748, has a mutation in the dnaJ gene, which codes for a "chaperonin." This defect has been shown to stabilize certain mutant proteins expressed in E. coli, e.g. the lacZ90 ochre fragment and mutants of lambda repressor. (dnaJ mutant with linked Tn10; from C. Gross via K. Silber; Straus et al. (1988) Genes Dev. 2:897-904; see also Reidhaar-Olson et al. (1990) Biochemistry 29:7563-7571).

This strain is defective in a periplasmic protease, which can cleave proteins that are overexpressed in the cytoplasm when the cells are lysed to make a crude extract. (tsp=tail specific protease, periplasmic protease cleaves the "tail" of a lambda repressor mutant); from K. Silber; Silber et al. (1992) PNAS USA 89:295-9)

This strain is deficient in an outer-membrane protease that cleaves between sequential basic amino acids (e.g. arg-arg). It can cleave proteins that are overexpressed in the cytoplasm when the cells are lysed to make a crude extract.   (CGSC7092; from B. Bachmann; Elish et al. (1988) J. Gen. Microbiol. 134: 1355-1364; Grodberg & Dunn (1988) J. Bacteriol 170:1245-1253;  Sugimura & Higashi (1988) J. Bacteriol 170:3650-3654).