SOS mutator DNA polymerase IV functions in adaptive mutation and not adaptive amplification.

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Adaptive mutations, including point mutations and amplifications, are crucial for bacterial survival under environmental stress.
• While adaptive mutation mechanisms exist in Escherichia coli, the specific enzymes involved remained largely unknown.

Purpose of the Study:

• To identify the enzymatic basis of adaptive point mutation in the Escherichia coli lac operon.
• To determine the role of SOS-inducible DNA polymerases in adaptive mutagenesis.

Main Methods:

• Utilized a nonpolar dinB mutation in Escherichia coli to assess its impact on adaptive mutation frequencies.
• Compared mutation rates in the lac operon under various conditions, including stress and normal growth.
• Evaluated the contribution of DNA polymerase IV (pol IV) and DNA polymerase III (pol III) to adaptive point mutations.

Main Results:

• A dinB mutation, which encodes pol IV, reduced adaptive point mutation frequencies by 85% in the lac operon.
• Pol IV deficiency did not affect adaptive amplification, growth-dependent mutation, or survival after UV or oxidative damage.
• Both pol IV and the major replicase, pol III, were found to be responsible for all adaptive point mutations observed at the lac locus.

Conclusions:

• DNA polymerase IV (pol IV) is a critical enzyme required for adaptive point mutations in Escherichia coli.
• Pol IV plays a specific role in inducible genetic changes that enhance bacterial adaptation to environmental stress.
• The findings elucidate the enzymatic machinery underlying stress-induced mutagenesis in bacteria.