Transcription Promoter

Question 1

What is the promoter sequence?

Answer 1

It is the binding site of RNA Pol

• Spans about 75 base pairs of DNA, most of which is not conserved (i.e. random)

Question 2

What are the major features of the E. coli promoter?

Answer 2

1. CAT (starting point)
2. TATA box/-10 sequence
3. -35 sequence
4. Spacing between -10 sequence and -35 sequence

Question 3

What is CAT?

Answer 3

 More than 90% of the time, the starting point (+1) is a purine located between 2 pyrimidines
 Correctly defined starting nucleotide: C/T A/G C/T

Question 4

What is the TATA box? What are its functions?

Answer 4

also known as -10 sequence
 Hexamer (6 bp) centred at about -10
 Sequence: TATAAT
 Found in many prokaryotes
 Functions
1. In contact with σ factor (the high binding affinity of σ is for TATAAT)
2. Mediates DNA melting: allows to form the transcription bubble
o Because it has weaker association: A-T only form 2 hydrogen bonds

Question 5

What is the -35 sequence?

Answer 5

 Conserved hexameric sequence: TTGACA

 Also recognized and bound by σ factor

Question 6

What is the spacing feature in the E. coli promoter?

Answer 6

between -10 sequence and -35 sequence
 16-18 bp
 -10 and -35 need to be on the same side of the helix of the DNA

Question 7

What sequences of promoter are found upstream of -35? What are their roles?

Answer 7

 They are variable

 Provide strength and facilitate elongation

Question 8

Why are there multiple σ factors?

Answer 8

 They recognize a specific promoter that codes for a limited number of genes