Two processivity clamp interactions differentially alter the dual activities of UmuC

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• DNA polymerases of the Y family are crucial for DNA repair and mutagenesis.
• Escherichia coli DNA pol V (UmuC) is key for UV and chemical mutagenesis and utilizes a beta processivity clamp-binding motif.

Purpose of the Study:

• To investigate the interaction sites between E. coli DNA pol V (UmuC) and the beta clamp.
• To elucidate the roles of these interaction sites in UmuC's functions, including mutagenesis and DNA damage checkpoint regulation.

Main Methods:

• Site-directed mutagenesis of the UmuC beta-binding motif and a second potential interaction site.
• Assessing UV-induced mutagenesis and cold-sensitive/synthetic lethal phenotypes.
• Analyzing the effects of compensatory mutations in the beta clamp.

Main Results:

• Mutations in the canonical UmuC beta-binding motif abolish UV-induced mutagenesis, partially rescued by wild-type beta.
• Alterations in this motif also disrupt cold-sensitive and beta-dependent synthetic lethal phenotypes.
• A second UmuC motif, corresponding to a second pol IV interaction site, is dispensable for mutagenesis but affects the cold-sensitive phenotype.
• Compensatory mutations in beta restored mutagenesis in a UmuC variant.

Conclusions:

• E. coli UmuC interacts with the beta clamp through at least two distinct sites.
• These interaction sites differentially regulate UmuC's functions in mutagenesis and DNA damage response.
• The beta clamp provides sophisticated management of DNA polymerase activity.