DnaGprimase

DnaG primase, commonly referred to as DnaG, is the bacterial primase responsible for synthesizing short RNA primers during DNA replication. It is the core component of the bacterial primosome, a multiprotein complex that also includes the helicase DnaB and other replisome factors. In many bacteria, including Escherichia coli, the primers produced by DnaG are about 8 to 12 ribonucleotides long and provide a free 3' hydroxyl group for DNA polymerase III to begin synthesis of the new strand. Primer synthesis is coupled to unwinding by DnaB, and DnaG activity is stimulated by its interaction with the helicase and coordinated with fork progression.

Structure and mechanism: DnaG contains regions that mediate interaction with DnaB and carry out RNA primer synthesis. A conserved zinc-binding motif participates in structural maintenance and protein–protein interactions within the replisome. The enzyme catalyzes template-directed RNA synthesis from ribonucleotide triphosphates in the presence of Mg2+ and initiates de novo, without a pre-existing primer.

Genetics and distribution: The dnaG gene encodes DnaG and is essential for chromosomal replication in most bacteria. DnaG is widely distributed among bacteria and represents the canonical bacterial primase; eukaryotes and archaea use different primase systems (for example, Pol alpha-primase in eukaryotes).