The Transcription Sites Of RNA Polymerase Ⅲ In The Nuclei Of CHO Cells Detected By FISH

The nuclei of eukaryotic cells contain three types of RNA polymerases: polymerase â… , â…¡ and â…¢. They perform different functions in the cells. RNA polymerase â…  synthesizes the three largest rRNAs, 5.8S , 18S and 28S rRNA. RNA polymerase â…¡ mainly produces mRNA encoding proteins, and RNA polymerase â…¢ makes 5S rRNA and tRNAs , as well as a few small nuclear RNAs.The transcription sites of the polymerases have been studied since early 1980s. The results of these early research work showed that RNA polymerase â…  transcription was localized in the nucleoli and RNA polymerase â…¡ and â…¢ in the nucleoplasm. Up until now, the active sites of RNA polymerase â…  and â…¡ transcription have been investigated thoroughly and the opinions were in line with each other. However, with the development and the application of new technologies since 1990s, the controversy arose on the transcription sites of RNA polymerase â…¢. In recent years, more and more scientists presumed that RNA polymerase â…¢ transcription might not occur in the nucleoplasm but in the nucleoli. Nevertheless, the possibility has not been proved directly.In this dissertation, the plasmids containing 5S promoter were transfected into CHO cells and the transcription sites of RNA polymerase â…¢ and its transcripts were detected by fluorescence in situ hybridization to DNA and RNA, respectively. It was showed under the laser scanning confocal microscopy that the transfected plasmid DNA transcripted by RNA polymerase â…¢ and its transcripts were both localized in the interior and periphery of nucleoli. It is inferred that its active transcription occurs in the same region, not the nucleoplasm. The result will help us to further comprehend the mechanism of RNA polymerase â…¢ transcription, the way of its transcripts processing and transport, and the structural and functional relationship among the three RNA polymeraes.