1、G5 Transcription in Eukaryotes: an OverviewG6 Transcription of Protein-Coding Genes in EukaryotesEach is responsible for the transcription of a certain groups of genes: rRNA, mRNA or tRNA genes.The enzymes are often identified by examining their sensitivity towards -amanitin （鵝膏蕈堿）（鵝膏蕈堿） (from a tox

2、ic mushroom). Type Localization Transcripts Effect towards -amanitin I Nucleolus 18S,5.8S, 28S rRNA Insensitive II Nucleoplasm mRNA snRNA Strongly sensitive III Nucleoplasm tRNA, 5S RNA Inhibited by high concentrations 鵝膏蕈堿鵝膏蕈堿Each of the three RNA polymerases contains 12 or more subunits, some of w

3、hich are similar to those of E. coli RNA polymerase. However, four to seven subunits in each enzyme are unique to that enzyme.2. Most protein-coding genes in eukaryotes are discontinuousMany Pol II promoters contain a TATAAA sequence (called a TATA box) at -25 position and an initiator sequence (Inr

4、) at +1 position.The preinitiation complex (including Pol II) is believed to assemble at the TATA box, with DNA unwound at the Inr sequence.However, many Pol II promoters lack a TATA or Inr or both sequences!General features of promoters for protein-codinggenes in higher eukaryotesGCboxCAATboxFirst

5、the TATA-binding protein (TBP) binds to the TATA box, then TFIIB, TFIIF-Pol II, TFIIE, and TFIIH (TFII, Factor for RNA polymerase II) will be added in order forming the closed complex at the promoter.TFIIH then acts as a helicase to unwind the DNA duplex at the Inr site, forming the open complex.A k

6、inase activity of TFIIH will phosphoryate the C-terminal domain of Pol II, which will initiate RNA synthesis and release the elongation complex.TFIIE and TFIIH will be released after the elongation complex moves forward for a short distance.Elongation factors will then join the elongation complex.Th

7、e termination of transcription of Pol II happens by an unknown mechanism.This basal process of initiating RNA synthesis by Pol II is elaborately regulated by many cell or tissue specific protein factors that will binds to the transcription factors, mostly act in a positive way.When Pol II transcription stops at a site of DNA lesion, TFIIH will binds at the lesion site and appears to recruit the entire nucleotide-excision repair