Multicopy suppression of cold-sensitive sec mutations in Escherichia coli

Area of Science:

• Molecular Biology
• Microbiology
• Genetics

Background:

• Mutations in secretory (sec) genes of Escherichia coli disrupt protein translocation across the inner membrane, often leading to conditional-lethal phenotypes.
• Chaperonins GroES and GroEL are crucial for protein folding and cellular homeostasis.

Purpose of the Study:

• To investigate the suppressive effect of GroES and GroEL overproduction on cold-sensitive sec mutations in E. coli.
• To elucidate the mechanism underlying this suppression and its relationship to the Sec pathway and protein synthesis.

Main Methods:

• Utilizing multicopy plasmids for overproduction of GroES and GroEL in E. coli strains with various sec mutations.
• Assessing suppression of cold-sensitive phenotypes and stimulation of precursor protein translocation.
• Investigating the role of the groE operon and unrelated protein overproduction in suppression.

Main Results:

• Overproduction of GroES and GroEL suppressed a broad range of cold-sensitive sec mutations, enhancing precursor protein translocation.
• Suppression was independent of the Sec pathway and the functional groE operon.
• Overproduction of unrelated proteins and protein synthesis inhibitors also suppressed sec mutations, suggesting a common mechanism.

Conclusions:

• Multicopy suppression of cold-sensitive sec mutations by GroES/GroEL is not dependent on the Sec pathway or the groE operon.
• The mechanism of suppression appears to involve a general compromise of protein synthesis, rather than direct involvement in protein export.