DNA Polymerase α Subunit Residues and Interactions Required for Efficient Initiation Complex Formation Identified by...

Area of Science:

• Molecular Biology
• Biochemistry
• Genetics

Background:

• DNA polymerase III holoenzyme (Pol III HE) is essential for bacterial DNA replication.
• Previous studies elucidated interactions between Pol III HE components and subassemblies.
• Understanding the initial steps of replication complex formation is critical.

Purpose of the Study:

• To identify residues and interactions vital for the ATP-dependent formation of the Pol III HE-primed DNA initiation complex.
• To characterize mutations affecting Pol III HE function using a dominant-negative genetic selection approach.

Main Methods:

• Genetic selection using a dominant-negative variant of the Pol III α subunit.
• Characterization of secondary mutations suppressing the dominant-negative phenotype.
• Purification and biochemical analysis of mutant proteins.

Main Results:

• Identified mutations in the PHP domain of Pol III α affecting ϵ subunit interaction and polymerase active site structure.
• Discovered mutations near the C-terminus disrupting τ subunit binding.
• Found mutations in the β-binding domain that reduced β2 processivity factor interaction and unexpectedly abolished τ binding.

Conclusions:

• The PHP domain of Pol III α is critical for ϵ subunit interaction and polymerase activity.
• The C-terminus and β-binding domain of Pol III α are involved in τ subunit interaction.
• The τ binding site on Pol III α is larger than previously anticipated, encompassing regions involved in β2 binding.