Effect of molecular and chemical chaperones on the solubility of recombinantly expressed proteins. GST was expressed using the pKK223 vector, GST-GFP by a gateway vector and the effect of DnaK (A) co-expression, 10 mM ectoine (B) and 5 mM betaine + 0.4 M NaCl (C) addition was measured. Soluble proteins were purified, the yields compared between control and treated samples and the variations induced by the growth condition modifications were calculated (control = 100%). D) β-galactosidase activity induced by the expression of GST and ClipA5 cloned into the pTrcHis2 vector and induced at 3 different temperatures either once with 100 μM IPTG or 3 successive times with 25 μM IPTG. All the experiments were repeated at least three times (SD < 4%).