三、 rRNa processing in eukaryotes 1, In the nucleolus, RNA polymerase I transcribes the rRNA, which usually exist in tandem repeats containing 100 or more copies of the transcription units 2\ Primary transcript 47S, containing ETS external transcribed sequence TS internal transcribed sequence ETS ITS ITS ETS Pre-18S Pre-58S Pre-28S二、rRNA processing in eukaryotes 1、In the nucleolus, RNA polymerase I transcribes the rRNA, which usually exist in tandem repeats containing 100 or more copies of the transcription units . 2、 Primary transcript 47S, containing ETS external transcribed sequence ITS internal transcribed sequence ETS ITS ITS ETS Pre-18S Pre-5.8S Pre-28S