Fig. 2.

Outline of the Escherichia coli variant strains built in this study and the expression of the groE operon in each of the strains under different conditions. K-12 MG1655 ΔmutS is a hypermutable strain lacking the DNA repair gene mutS obtained from K-12 MG1655. The plasmids pGro7 (Takara Inc. # 3340) and pΔgroE (modified from pGro7) were introduced in K-12 MG1655 ΔmutS, obtaining the strains pgroE and pΔgroE. The strain pgroE presents a higher level of GroEL than the wild type, corresponding to the 15-plasmid copies containing groE operon and basally expressed, when grown in media without inducer (−). In the presence of the inducer l-arabinose (+), groE is overexpressed several orders of magnitude above the constitutive level. The control lines pΔgroE contain the plasmid lacking the operon groE, otherwise is identical to all other strains. Western images correspond to lines grown at 37 °C. GroEL is stained using monoclonal antibodies.