The enzyme responsible for catalyzing the formation of an RNA primer is primase.

Here's why:

* DNA polymerase can only add nucleotides to an existing strand of DNA. It needs a starting point.

* Primase is a type of RNA polymerase that synthesizes a short RNA sequence called a primer.

* This primer provides the 3' hydroxyl group that DNA polymerase needs to begin adding nucleotides to the new DNA strand.

Let me know if you have any other questions!