Eukaryotic Transcription

• Eukaryotic transcription has more complex regulation
• Complex regulation of transcription enables each cell of eukaryotes to have distinct functions
• Eukaryotic transcription involves three types of RNA polymerase
• Eukaryotic transcription involves complex promoter elements
• RNA processing occurs during eukaryotic transcription
• RNA processing involves

  • Modification to the 5' and 3' ends of the transcript
  • Splicing out non-coding regions
• Spatial and temporal separation occurs between transcription and translation for eukaryotes
• Transcription occurs in the nucleus
• Translation occurs in the cytoplasm
• In prokaryotes, transcription and translation are coupled and occur in the same space
• RNA Polymerase I is found in the nucleolus
• what are the transcripts of RNA Polymerase I?

  rRNA
• RNA Polymerase II occurs in the nucleoplasm
• what are the transcripts of RNA Polymerase II?


  mRNA precursors and snRNA
• RNA Polymerase III occurs in the nucleoplasm
• what are the transcripts of RNA Polymerase III?


  tRNA and 5S rRNA
• The nucleolus resides within the nucleus and is the site of ribosome biogenesis
• snRNA is involved in splicing
• high levels of RNA Polymerase II are required for transcription
• Promoters are always on the same DNA molecule as the gene they regulate
• Eukaryotic promoters differ in sequence and position relative to the regulated genes
• Promoters can be at the start site, upstream or downstream
• Various promoters can combine
• Promotors for RNA Polymerase II are generally on the 5' side of the start site
• TATA Box is centred at -25
• CAAT box and GC box are located between -40 and -150
• Positions of these CAAT box and GC box vary a lot
• CAAT box and GC box can be found on either the template or coding strand
• Inr is centred at +1 (the initiation site)
• Initiator element = Inr
• Inr can compensate for an absent/degenerate TATA box
• Inr defines the start site
• Downstream core promoter elements are centred at +30
• Downstream core promoter element are commonly found in conjunction with the initiator element in genes lacking the TATA box
• Unlike bacterial promoters, eukaryotic promoter elements are recognised by proteins rather than RNA polymerase itself
• Enhancer sequences are DNA sequences that stimulate transcription but do not have promoter activity on their own
• Enhancer sequences can exert stimulatory action over a large distance
• Enhancer sequences can be upstream, downstream, or in the middle of a transcribed gene
• Enhancer sequences can be present on either DNA strand
• TFs are proteins that bind to promoter/enhancer elements to help recruit RNA polymerase