L12: Eukaryotic Transcription

• Where do bacterial transcription and translation occur?

  In the same compartment of the bacterial chromosome
• How are bacterial mRNAs generally modified?

  They are generally not modified, but some like rRNA and tRNA are processed from a primary transcript
• What happens to eukaryotic transcripts after they are produced?

  They are processed and transported to the cytosol
• What modifications occur to the primary transcript in eukaryotes?

  The primary transcript is capped at the 5' end, spliced to remove introns, and polyadenylated at the 3' end
• How many main RNA polymerases are there in eukaryotes?

  There are three main RNA polymerases
• What is the primary function of RNA Polymerase II in eukaryotes?

  It transcribes mRNAs
• What characterizes eukaryotic RNA polymerases compared to bacterial RNA polymerase?

  Eukaryotic RNA polymerases are complex and have multiple subunits
• What is required for eukaryotic transcription initiation?

  Multiple additional proteins called general transcription factors
• How does the chromatin structure affect eukaryotic transcription?

  Higher order chromatin structures need to be unwound for transcription
• What is the TATA box in eukaryotic promoters?

  It is an upstream sequence usually located between -30 and -100 from the transcriptional start
• How do bacterial and eukaryotic promoter sequences differ?

  Bacterial promoters have -10 and -35 sequences, while eukaryotic promoters have TATA and CAAT sequences
• What is a significant evolutionary aspect of eukaryotic cells compared to Archaea?

  Eukaryotes have multiple RNA polymerases, while Archaea have one RNA polymerase
• How does histone acetylation affect transcription?

  It promotes a loose chromatin structure that permits transcription
• What is the role of TFIID in transcription initiation?

  TFIID guides RNA Pol II to its promoters
• What is the composition of the TFIID complex?

  It comprises 11 TAFs and the TATA-box binding protein (TBP)
• What is the basal transcription apparatus?

  It is the complex formed by TFIID, TBP, and other transcription factors necessary for initiation
• How do enhancers function in gene transcription?

  Enhancers increase transcription levels and can be several kb away from the transcription start site
• What role do mediator proteins play in transcription regulation?

  Mediator proteins act as a bridge between activator proteins and RNA Pol II
• What is the function of enhancer and silencer elements in gene expression?

  Enhancers turn genes 'on' while silencers turn genes 'off'
• How does combinatorial control of gene activation work with enhancers?

  Transcription can only be enhanced if the appropriate activators are present
• What is Burkitt’s lymphoma associated with in terms of gene regulation?

  It is associated with inappropriate regulation of the MYC oncogene by a strong enhancer
• What are the two functions of TFIIH during transcription initiation?

  TFIIH acts as a helicase to open the DNA double helix and as a kinase to phosphorylate the CTD of RNA Pol II
• What happens during the elongation phase of transcription?

  RNA is synthesized and RNA Pol II progresses, freeing the promoter for further recruitment
• What is the effect of α-amanitin on RNA polymerase II?

  It inhibits elongation by binding tightly to the active site of RNA Pol II
• What are the three modifications that occur to RNA Pol II transcripts?

  They are capped at the 5' end, spliced to remove introns, and polyadenylated at the 3' end
• How is the 5' cap added to eukaryotic mRNA?

  The 5' triphosphate is modified to form a 5'-5' triphosphate linkage with methylation of the terminal guanine
• What is the role of the poly(A) tail in mRNA?

  The poly(A) tail is important for the stability of mRNA and is added after cleavage of the primary transcript
• How do capping and tailing enzymes locate the transcript?

  Phosphorylated CTD recruits the capping enzyme and other processing enzymes
• What occurs during the termination of transcription for RNA Pol II?

  The rate of transcription slows, the poly A site is cut, and RNA Pol II disengages from the DNA
• What is the primary difference between bacterial and eukaryotic mRNA transcription?

  Bacterial mRNAs are often polycistronic, while eukaryotic mRNAs are monocistronic