RNA polymerase enzyme catalyses the synthesis of RNA. It is single in prokaryotes. There are three types of RNA polymerases in eukaryotes- I for 28S,18S and 5.8S RNA, II for mRNA and snRNA and III for tRNA, 5SRNA and scRNA. Primase is an RNA polymerase that is used to initiate DNA synthesis: RNA ligase reunites the exon segment after RNA splicing.