RNAprimase

RNA primase is an enzyme that synthesizes short RNA primers de novo using a DNA template, providing a free 3'-OH end for DNA polymerases to begin elongation. It plays a central role in initiating DNA synthesis on both leading and lagging strands during replication, with a particular importance for the discontinuous synthesis of the lagging strand.

In bacteria, the primase is typically a single enzyme known as DnaG, which forms part of the primosome together with the helicase DnaB. DnaG initiates RNA primer synthesis, producing primers usually around 10 nucleotides long. The RNA primer is then extended by DNA polymerase III, after which the primer is replaced and gaps are filled by other enzymes.

In archaea and eukaryotes, primase is part of a larger multi-subunit complex called the DNA polymerase alpha-primase complex. The primase component consists of small PriS and large PriL subunits. This complex first lays down an RNA primer of about 10 nucleotides, after which DNA polymerase alpha extends the primer with a short DNA segment, enabling further elongation by the main replicative polymerases.

Primer removal and replacement differ by domain. In bacteria, DNA polymerase I removes the RNA primer and fills the gap with DNA, with DNA ligase sealing the nick. In eukaryotes, RNase H and FEN1 remove the RNA primer, and polymerase delta or epsilon fills the gap before ligation.

RNA primase is essential for DNA replication and genome stability. It is of interest as a potential target for antibacterial strategies due to differences between bacterial and eukaryotic primases.