Studies on a factor enhancing colicin E3 activity in vitro.

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• Colicin E3 (E3) is a bacteriocin known to inhibit protein synthesis by cleaving 16S ribosomal RNA (rRNA).
• The precise mechanism and factors influencing E3's activity, particularly its ribosome inactivation and bactericidal effects, require further elucidation.
• Standard E3 preparations exhibit both ribosome-inactivating and bactericidal activities, but their relationship is not fully understood.

Purpose of the Study:

• To investigate the in vitro mechanism of action of colicin E3 (E3) on bacterial ribosomes.
• To identify factors that modulate E3's ribosome-inactivating and bactericidal activities.
• To determine if E3's activities are mediated by the native colicin molecule or a modified form.

Main Methods:

• In vitro assays using purified and crude/washed ribosomes from Escherichia coli.
• Fractionation of E. coli cell supernatant to isolate potential co-factors.
• Incubation of E3 with isolated factors and subsequent heat treatment.
• Quantification of ribosome inactivation and bactericidal activity.

Main Results:

• Purified ribosomes were less susceptible to E3 than crude or washed ribosomes.
• A supernatant factor from E. coli significantly stimulated E3-mediated ribosome inactivation, reducing the required E3 amount tenfold.
• Heating E3 with this factor dramatically increased ribosome-inactivating activity (6x10^4-fold increase in ratio) while decreasing bactericidal activity.
• The heat-treated product cleaved 16S rRNA similarly to native E3.

Conclusions:

• Ribosome inactivation by E3 is potentiated by a factor present in E. coli supernatant.
• The ribosome-inactivating and bactericidal activities of E3 are distinct and do not correlate directly.
• Standard E3 preparations may not fully represent the active form; a modified E3, likely generated in the presence of the cellular factor and heat, is responsible for potent ribosome inactivation.