Process of replication needs a set of enzymes. The main enzyme is DNA dependent DNA polymerase. If uses a DNA template to catalyze the polymerization of deoxyribonucleotides. There is single DNA dependent RNA polymerase that catalyzes the transcription of all types of RNA in bacteria. RNA polymerase binds to promoter and initiates transcription (initiation). Here, truely speaking, RNA polymerase is only capable of catalysing the step of elongation. It associates transiently with 'initiation factor' and "termination factor' to initiate and terminate the transcription. In eukaryotes, there are three RNA polymerases in the nucleus. The RNA polymerase I transcribes rRNA (28s, 18s and 5.8s). RNA polymerase III is responsible for transcription of tRNA, 5sr RNA and snRNA (small nuclear RNAs). The RNA polymerase II transcribe precursor of mRNA and heterogenous nuclear RNA (hnRNA). Thus there is clear cut division of labour.
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