An enzyme that creates the short primer sequences needed for the discontinuous replication of DNA. It is an RNA polymerase that synthesizes a short segment of RNA, consisting of 10 to 12 nucleotides, attached to the lagging strand of the unwound DNA molecule. Each primer sequence provides the free 3′-OH group required for the initiation of synthesis of an Okazaki fragment by DNA polymerase. These primers are subsequently removed before the Okazaki fragments are united into a continuous new DNA strand. See also primosome.