Figure 2

Schematic diagram of the molecular and physiological responses during thermoinduction. When cultures are induced upon a temperature increase, σ32 transcription is enhanced. σ32 regulates the expression of hsp, directing the RNA polymerase (RNAP). σ32 activity is controlled by negative feedback through binding to DnaK/J and GroEL/S, whereas it is degraded FtsH. Over-synthesis of hsp initiates the negative feedback control of σ32. Temperature up-shift from 30°C to 34°C initiates the induction of hsp synthesis [23]. Up to 37°C, cI857 repressor is released from the pL/pR promoters and recombinant protein transcription starts. The nascent polypeptides need the assistance of chaperones for correct folding, but some of them remain as unfolded intermediate until their aggregation. Under severe stress conditions, large aggregates can be formed. Reaching 42°C and/or the overproduction of heterologous protein can cause important stresses and metabolic unbalances, generating a global stress response, diminishing growth, and triggering the stringent and the SOS responses. RP: recombinant protein, hsp: heat shock proteins. TF: chaperone trigger factor.