Now the next step is to basically form that other strand, the complementary strand to this cDNA molecule. And before we actually add the DNA polymerase so that it can synthesize the complementary strand, we have to once again create a primer. The problem is we don't know what this sequence here is. And so what we do is we use a special enzyme that adds a specific sequence of nucleotides onto the three prime end that we know. And so we add an enzyme called terminal transferase. And this catalyzes the addition of specific types of nucleotides.