2.1 Transcription in eukaryotic genes

Properties of eukaryotic transcription

• Complex!
• RNA polymerase is the main protein that creates the RNA transcript
• Proteins called transcription factors help RNA polymerase and regulate it's function.
• 2 types of transcription factors: basal tfs and modulatory tfs.
• Basal transcription factors - required for all transcription events.
• Modulatory transcription factors - regulate expression of genes. Both positive and negative regulation.
• Transcription factors can act from relatively far away. Up to 10kb!
• pre-mRNA transcripts are spliced to remove exons.
• Alternative splicing allows the cell to combine exons differently in the final mRNA transcript from the same pre-mRNA transcript.

Transcription in five easy steps

• Transcription of DNA to pre-mRNA. DNA, RNA polymerase and transcription factors.
• Addition of 5' methyl guanosine cap to pre-mRNA transcript.
• Splicing of pre-mRNA transcript (yields mRNA proper)
• Addition of 3' poly(A) tail to mRNA transcript.
• mRNA is transported to the cytoplasm.

Rna polymerase - main protein that creates rna transcript.

RNA polynmerase is the protein whose job it is to 'read' the genetic code and create a complimentary RNA transcript from that code. Eukaryotes have three different types of RNA polymerases: RNA polymerase I, II, and III. RNA polymerase II is the from of polymerase that transcribes most genes and is the form of polymerase with which we need to concern ourselves.

Initiation of transcription

Transcription initiation in eukaryotes is complicated, and the details are not entirely understood (although we do have a good grasp on the basic mechanism). The fully assembled eukaryotic transcription inititation complex contains more than 50 polypeptides. RNA polymerase II has more than 10 polypeptide subunits by itself. Keep in mind that the process outlined below is a generalization, and any given, specific transcription event will probably vary some in the details. For example, although the TATA box is the most strongly conserved promoter sequence, it is by no means present in every eukaryotic promoter. Also, there is some debate as the importance of the order of the binding of the proteins in the initiation complex: it was thought that a specific order was vital, now, however, new evidence suggests that reaching the end binding state may be what is really important, whatever the order.

Transcription factors - help/regulate rna polymerase's function