RNA polymerases from both prokaryotes and eukaryotes catalyze the synthesis of RNA from the DNA template. There is only one kind of RNA polymerase in bacteria, whereas there are several kinds in eukaryotes; however, they all share a common structure (Figure 14.3). Like DNA polymerases, RNA polymerases catalyze the addition of nucleotides in a 5′-to-3′ direction and are processive; that is, a single enzyme–template binding event results in the polymerization of hundreds of RNA bases. But unlike DNA polymerases (see Figure 13.11), RNA polymerases do not require a primer.