DNA synthesis begins, therefore, by synthesizing a short segment of RNA called a primer, which primer is synthesized by an enzyme called Primasa. Primasa is an RNA polymerase that uses DNA as a template. All fragments of Okazaki begin with a Primer. Subsequently, the DNA polymerase III Holoenzyme performs the synthesis of the corresponding DNA fragment until it reaches the next primer. At that time, DNA polymerase Ia replaces the DNA polymerase Holoenzyme III. The DNA polymerase I is responsible for removing the RNA primer through its 5'P-3'OH exonueotic activity and at the same time fills the hole by synthesizing DNA.
Finally, the two Okazaki fragments have to be joined, it is necessary to link the 3'OH end of a fragment with the 5'P of the next fragment. This work of sealing and joining the successive fragments is done by Ligase.
