transcription process in eukaryotes their factors RNA polymerase enzyme an intiation elongation termination process

1. TRANSCRIPTION IN EUKARYOTES
Mrs. Praveen garg
VITS College, Satna

2. INTRODCTION
• Eukaryotic transcription is the process that eukaryotic cells use
to copy genetic information stored in DNA into
complementary RNA.
• Unlike prokaryotic RNA polymerase, In eukaryotes, there are
three RNA polymerase.
• A eukaryotic cell has a nucleus that separates the processes of
transcription and translation.
• Eukaryotic transcription occurs within the nucleus where DNA
is packaged into nucleosomes and higher
order chromatin structures.

4. Name Location Product
RNA Polymerase I (Pol I,
Pol A)
nucleolus
larger ribosomal RNA
(rRNA) (28S, 18S, 5.8S)
RNA Polymerase II (Pol II,
Pol B)
Nucleus
messenger RNA (mRNA),
most small nuclear RNAs
(snRNAs), small interfering
RNA (siRNAs) and
microRNA (miRNA).
RNA Polymerase III (Pol
III, Pol C)
nucleus (and possibly the
nucleolus-
nucleoplasm interface)
transfer RNA (tRNA), other
small RNAs (including the
small 5S ribosomal RNA (5s
rRNA), snRNA.
TYPES OF RNA POLYMERASE

5. EUKARYOTIC PROMOTERS
• The promoters recognized by RNA Polymerase II are larger and
diverse.
 GC Box: These are structural gene, expressed in all tissues, also
called as house keeping gene having sequence GGGCGG located
upstream to transcription start site.
 TATA Box: It is structural gene present 25 to 30bp upstream to
the start site, has consensus sequence TATAAAA.
 CAAT Box: It has GGCCAATCT sequence. It is located 70 to
80bp upstream to start site.
 Octamer Box: It is present in the RNA polymerase II promoter
and has consensus sequence ATTTGCAT. It influence the
efficiency of promoter to initiate transcription.

6. Promoter for RNA Polymerase II

7. • Eukaryotic genes also contain regulatory sequences with the core
promoter. These regulatory elements bind transcriptional
activators or repressors to increase or decrease transcription from
the core promoter.
• These regulatory elements include enhancers, silencers.
• These regulatory sequences can be spread over a large genome,
sometimes located hundreds of kilobases from the core promoters.
• These factors have DNA-binding domains that bind specific
sequence elements of the core promoter and help recruit RNA
polymerase to the transcriptional start site.
• The position of the enhancers can be either upstream or
downstream.
Regulatory sequence

9. • Transcription factors are a group of proteins involved in
transcription initiation and regulation with RNA polymerase.
• Transcription factor are responsible for recognizing the promoter
for all RNA polymerase.
• Initiation of transcription involve many protein-protein
interaction among transcription factor bound at the promoter or
at the enhancer with RNA polymerase.
• There are four type of transcription factor:
 Basal factors: required for synthesis of all mRNA.
 Activators: bind directly to DNA at promoter or the enhancer.
 Coactivators: bind to both activators and basal apparatus.
 Regulators: acts on chromatin structure.
TRANSCRIPTION FACTOR

10. Basal transcription factor
• These factors required for initiation, it recognize initiation site
and delivers RNA polymerase II to form a initiation complex.
• There are various transcription factor:
TFIIA, TFIIB, TFIID, TFIIE, TFIIF, TFIIH
• TFIIA: Stabilizes TBP and TAF binding
• TFIIB: Stabilizes TBP binding, influence start site selection
• TFIID: Recognize TATA box, recruit TFIIA and TFIIB, has
positive and negative regulatory functions.
• TFIIE: It is heterotetramer consist of 2α&2β unit, recruit TFIIH
and stimulate its helicase activity; enhancer promoter melting.
• TFIIF: Facilitates promoter targetting stimulates elongation,
recruit RNA polymerase II.
• TFIIH: Contain an ATP- dependent helicase that function in
promoter melting and clearence.

11. Transcription factor and RNA Polymerase- II
bind with promoter

12. Activators
• Activators are the transcription factors that bind to specific DNA
sequences (GC box, CAAT box) upstream of the initiation site to
stimulate or repress.
• They also bind to site in the promoter or in enhancer.
• They increase the efficiency of transcription and are required for
a promoter to function properly.
• Some activators act constitutively, whereas others have a
regulatory role and are synthesized or activated at specific time or
in specific tissues.
• These factor are responsible for control of transcription pattern.

13. Activator have two independent domain
DNA binding domain Activating domain

14. • The role of DNA binding domain is to bring the transcription
activation domain into the vicinity of promoter.
• Transcription activating domain work by making protein-
protein contacts with transcription factor.

15. Co-activators
• Members are another group of factors necessary for efficiency of
transcription do not themselves bind DNA.
• Co-activators provide a connection between activators and the
basal apparatus.
• They work by protein-protein interaction and forming a bridges
between activators and basal apparatus.

16. • In the process of initiation, transcription factors firstly bind to the
promoter region and then help recruit the appropriate RNA
polymerase.
• The completed assembly of transcription factors and RNA
polymerase bind to the promoter, forming a transcription pre-
initiation complex (PIC).
• The TATA box, as a core promoter element, is the binding site for a
transcription factor known as TATA-binding protein (TBP), a
subunit of another transcription factor: TFIID.
• After TFIID binds to the TATA box via the TBP, five more
transcription factors and RNA polymerase combine around the
TATA box in a series of stages to form a pre-initiation complex.
INITIATION OF TRANSCRIPTION

17. Formation of Pre-Initiation Complex

18. • TFIIH is involved in separating opposing strands of double-
stranded DNA to provide the RNA Polymerase access to a single-
stranded DNA template.
• Other proteins known as activators and repressors, along with
coactivators or corepressors, are responsible for modulating
transcription rate.
• Activator proteins increase the transcription rate, and repressor
proteins decrease the transcription rate.

19. • RNA Polymerase II is a complex of 12 protein subunits. Specific
subunits allow RNA Polymerase II to act as its own helicase,
sliding clamp, single-stranded DNA binding protein, as well as
carry out other functions.
• Transcription elongation occurs in a bubble of unwound DNA,
where the RNA Polymerase uses one strand of DNA as a template
to catalyze the synthesis of a new mRNA strand in the 5′ to 3′
direction.
• Early in the elongation process, the 5’ end of the pre mRNA are
modified by the addition of 7- methyl guanosine (7-MG) caps.
• The 7- MG caps are added when the growing RNA chain are only
30 nucleotide long.
• It helps to protect mRNA chain from degradation by nucleases.
• This process continues until transcription termination occurs.
ELONGATION OF TRANSCRIPTION

20. 7-MG

21. • The 3’ ends of RNA transcripts synthesized by RNA polymerase II
are produced by endonucleolytic activity cleavage of the primary
transcript.
• Transcription termination occur in downstream site from the start
point that will become 3’ end of the mature transcript.
• Towards 3’ end of the primary transcript usually contain
nucleotides sequence AAUAAA, consensus sequences, which help
in cleavage process of pre mRNA.
• After cleavage the enzyme poly A polymerase adds poly A tail, to
the 3’ end of transcripts.
• The addition of poly A tail to mRNA is called polyadenylation.
• This process play a important role in their transport from the
nucleus to the cytoplasm.
TERMINATION OF TRANSCRIPTION

23. THANK YOU