GIGUERE - LECTURE 1 Flashcards
prokaryotic vs eukaryotic transcription
transcription in prokaryotes characteristics
what are the four steps of transcription in prokaryotes
structure of the prokaryotic RNA polymerase
all RNA prokaryotes are transcribed by this single RNA polymerase
what is the size and the subunits of the RNA polymerase
400kD total size
5 subunits: 2 alpha (each 35kD), beta (124kD) and beta prime (171kD) as well as the sigma subunit
what are the functions of the alpha and beta subunits on the RNA polymerase?
what is the function of the sigma subunit
sigma subunits binds to beta prime
allows RNA polymerase to recognise different DNA sequences that act as promoters
dissociation of the sigma subunit from the enzyme allows the core polymerase to make DNA into RNA
the core enzyme is unable to recognise promoters and start transcription without the sigma subunit
what are promoters
what is step 1 of prokaryotic transcription
binding of RNA polymerase to the promoter
the beta subunit recognises it
the RNA polymerase bound to the promoter forms a closed promoter complex
the promoter region typically spans from -70 to +20 nucleotides
last step of step 1: unwinding by the sigma subunit of 14 base pairs of DNA located at -12 to +2 relative to the start (open promoter complex)
properties of prokaryotic promoters
prokaryotic promoters and the sigma subunit
ribosomal RNA gene (rrn) and its promoter
transcription of rrn genes is more than 60% of total RNA synthesis in quickly growing E.coli cells
highly expressed rrn genes in E.coli have an additional third sequence in its promoters: upstream element (UP element), located 20bp immediately upstream of the -35 region
the C-terminal domains (CTD) of the alpha subunits of RNA polymerase recognise and bind the UP element
how does step 2 of transcription happen
initiation of polymerisation
1. RNA polymerase has 2 binding sites for NTPs: initiation and elongation
2. first nucleotide binds at the initiation site
3. second incoming nucleotide binds to the elongation site
4. once a 9-12 nucleotide residue is made, the sigma subunit dissociates, which completes initiation
5. the core polymerase is highly processive and continues, with the DNA duplex unwinding ahead of it
what is abortive initiation of transcription
what is the error rate of prokaryotic RNA polymerase
what are the two types of transcription termination mechanisms in bacteria?
- intrinsic (rho independent)
- rho dependent
rho independent termination
rho dependent termination
