Transcribes specific genes o sigma interacts with

Transcribes specific genes
o Sigma interacts with tetrameric core to recognize promoter in order to
start transcription at the beginning of the gene
 Funtions of the subunits:
o α: assembly of the tetrameric core
o β: ribonucleotides triphosphate binding site
o β’: DNA template binding region
o σ: initiation of transcription specifically at a promoter
Initiation of Transcritption
 Initiates about 5-9 base pairs down from the end of the -10
sequence
 The 5’ end for the RNA is usually a purine
 +1 position: First purine (T or C) after the -10 sequence
o Will start copying from T or C and A or G will be the
first base in the new strand
 Structure of promoter: 2 block sequence information – 10 sequence and -35
sequence
 Sequences are known as consensus sequences- found
most often in these positions
o -10 sequence: Very A/T rich  localized unwinding
occurs here
 5’ TATAAT 3’
 “Pribnow” Box
o -35 sequence: σ factor binding site is here
 5’ TTGACA 3’
 4 different ways to orient the duplex, you will need to go in from 5’ ends
(might not be given, have to find the -35 sequence to know which is the 5-3
strand)

MBG*2040 Exam Notes December 2015
Elongation
 Basic mechanism
 Synthesis proceeds 5’-3’
 Grows one base at a time
 The Transcription Bubble:
 Area where transcription elongation takes place
 RNA polymerase has helix unwinding and rewinding
activities
Rho- Independent or Intrinsic Termination- Prokaryotes only
 Rho- D: Protein that catches up to RNA polymerase
when it pauses and stops it  Eukaryotes only
o Has to tell it where to stop, or it would go on
forever
o Sequences in DNA which get made into
RNA which tell RNA polymerase to stop
 Common mechanism in bacteria
 Weak H-bonding at U:A residues allows mRNA release from DNA when
polymerase pauses at termination
 Polymerase recognizes that hairpin is formed and pauses it from
transcription. When polymerase pauses they come apart and transcription
stops
 Green match up and can
pair with each other,
they are self-
complementary, can
form hairpin structure
 Hairpin structure causes
polymerase to pause.
Weak U-A bonds result in
its release

MBG*2040 Exam Notes December 2015
Transcription and Translation are Tightly Coupled in E. coli
 Fibres come off somewhat perpendicular, chains of blobs represent mRNA
that are being made by RNA polymerases and are transcribing genes,
blobs represent ribosomes
 Can tell which way the polymerase has gone depending on the length of
the mRNA chains
o The shorter the chain, the closer it is to the 3’ end of the DNA
o The longer the chain, the further it is from the 3’ end of DNA
Transcription and RNA processing in Eukaryotes
 Polytene: many double stranded DNA strands that
have copied but stay together
 Puffs in chromosomes: sites of localized unwinding
due to gene transcription
o Can open where transcription is occurring and
they can close
 Regions of chromosomes where tightly compacted
chromatin have made loops