Archaeal/eukaryotic core primase: Large subunit, PriL
Primases synthesize the RNA primers required for DNA replication. Primases are grouped into two classes, bacteria/bacteriophage and archaeal/eukaryotic. The proteins in the two classes differ in structure and the replication apparatus components. The DNA replication machinery of archaeal organisms contains only the core primase, a simpler arrangement compared to eukaryotes. Archaeal/eukaryotic core primase is a heterodimeric enzyme consisting of a small catalytic subunit (PriS) and a large subunit (PriL). Although the catalytic activity resides within PriS, the PriL subunit is essential for primase function as disruption of the PriL gene in yeast is lethal. PriL is composed of two structural domains. Several functions have been proposed for PriL, such as the stabilization of PriS, involvement in the initiation of synthesis, the improvement of primase processivity, and the determination of product size.