Three types of RNA polymerase in eukaryotic （三种类型的RNA聚合酶在真核生物）.pdf

Three types of RNA polymerase in eukaryotic nuclei Type Location RNA synthesized Effect of α-amanitin I Nucleolus Pre-rRNA for 18, 5.8 and 28S rRNAs Insensitive II Nucleoplasm Pre-mRNA, some snRNAs Sensitive to 1 µg/ml III Nucleoplasm Pre-tRNAs, 5S rRNA, some snRNAs Sensitive to 10 µg/ml • α-amanitin from Amanita Phalloides binds tightly to RNA Pol II and blocks transcriptional elongation. • RNA Pol I transcribe 1 gene at ~200 copies. The gene for the 45S pre-rRNA is present in tandem array. • RNA Pol II transcribe ~25,000 genes; • RNA Pol III transcribe 30-50 genes at variable copy numbers. (Also- Organelle RNAPs in Mitochondria and Chloroplasts. Encoded by organelle genomes. Similar to bacterial RNAPs.) Subunit composition of eukaryotic RNA polymerases •All three yeast polymerases have five core subunits that exhibit some homology with the β, β‘, α and ω subunits in E. coli RNA polymerase. •RNA polymerases I and III contain the same two non-identical α-like subunits, whereas polymerase II has two copies of a different α-like subunit. •All three polymerases share four other common subunits. In addition, each RNA polymerase contains three to seven unique