DnaQ

dnaQ is a gene found in many bacteria that encodes the epsilon subunit of DNA polymerase III, the main enzyme responsible for chromosomal DNA replication. In Escherichia coli, dnaQ is also known as mutD, a name that reflects its role in maintaining replication fidelity.

The primary function of the DNA polymerase III epsilon subunit is 3′ to 5′ exonuclease proofreading. As DNA is synthesized, the epsilon subunit removes incorrectly paired nucleotides from the nascent strand, allowing the polymerase to reinsert the correct bases. This proofreading activity greatly increases the accuracy of DNA replication and works in concert with the polymerase core and other replisome components, such as the theta subunit, to ensure high-fidelity DNA synthesis. The protein belongs to the DnaQ-like family of proofreading exonucleases, which share conserved catalytic motifs.

Genetically, dnaQ is conserved across many bacterial species, and its proper function is important for maintaining low mutation rates. Loss or impairment of dnaQ proofreading activity often results in a mutator phenotype, characterized by a higher rate of spontaneous mutations. Such mutants are useful in research to study mutation processes and evolution, and dnaQ mutants have been observed to accumulate genetic changes more rapidly than wild-type strains. In some contexts, mutD/dnaQ alleles can influence the balance between replication accuracy and adaptability.

In summary, dnaQ encodes the epsilon subunit of DNA polymerase III, providing essential 3′ to 5′ proofreading activity that enhances replication fidelity in bacteria.