<< Chapter < Page Chapter >> Page >

A scientist characterizing a new gene can determine which polymerase transcribes it by testing whether the gene is expressed in the presence of a particular mushroom poison, α-amanitin ( [link] ). Interestingly, α-amanitin produced by Amanita phalloides , the Death Cap mushroom, affects the three polymerases very differently. RNA polymerase I is completely insensitive to α-amanitin, meaning that the polymerase can transcribe DNA in vitro in the presence of this poison. In contrast, RNA polymerase II is extremely sensitive to α-amanitin, and RNA polymerase III is moderately sensitive. Knowing the transcribing polymerase can clue a researcher into the general function of the gene being studied. Because RNA polymerase II transcribes the vast majority of genes, we will focus on this polymerase in our subsequent discussions about eukaryotic transcription factors and promoters.

Structure of an rna polymerase ii promoter

Eukaryotic promoters are much larger and more complex than prokaryotic promoters, but both have a TATA box. For example, in the mouse thymidine kinase gene, the TATA box is located at approximately -30 relative to the initiation (+1) site ( [link] ). For this gene, the exact TATA box sequence is TATAAAA, as read in the 5' to 3' direction on the nontemplate strand. This sequence is not identical to the E. coli TATA box, but it conserves the A–T rich element. The thermostability of A–T bonds is low and this helps the DNA template to locally unwind in preparation for transcription.

Illustration shows a series of transcription factors binding to the promoter, which is upstream of the gene. After all of the transcription factors are bound, RNA polymerase binds as well.
A generalized promoter of a gene transcribed by RNA polymerase II is shown. Transcription factors recognize the promoter. RNA polymerase II then binds and forms the transcription initiation complex.

Art connection

An illustration shows that before RNA processing, there is a primary RNA transcript including five boxes labeled, left to right, as exon 1, intron, exon 2, intron, and exon 3. After RNA processing, there is a spliced RNA with these parts, left to right: a 5' cap, a 5' untranslated region, exon 1, exon 2, exon 3, a 3' untranslated region, and a poly-a tail.
Eukaryotic mRNA contains introns that must be spliced out. A 5' cap and 3' poly-A tail are also added.

A scientist splices a eukaryotic promoter in front of a bacterial gene and inserts the gene in a bacterial chromosome. Would you expect the bacteria to transcribe the gene?

The mouse genome includes one gene and two pseudogenes for cytoplasmic thymidine kinase. Pseudogenes are genes that have lost their protein-coding ability or are no longer expressed by the cell. These pseudogenes are copied from mRNA and incorporated into the chromosome. For example, the mouse thymidine kinase promoter also has a conserved CAAT box    (GGCCAATCT) at approximately -80. This sequence is essential and is involved in binding transcription factors. Further upstream of the TATA box, eukaryotic promoters may also contain one or more GC-rich boxes (GGCG) or octamer boxes (ATTTGCAT). These elements bind cellular factors that increase the efficiency of transcription initiation and are often identified in more “active” genes that are constantly being expressed by the cell.

Transcription factors for rna polymerase ii

The complexity of eukaryotic transcription does not end with the polymerases and promoters. An army of basal transcription factors, enhancers, and silencers also help to regulate the frequency with which pre-mRNA is synthesized from a gene. Enhancers and silencers affect the efficiency of transcription but are not necessary for transcription to proceed. Basal transcription factors are crucial in the formation of a preinitiation complex    on the DNA template that subsequently recruits RNA polymerase II for transcription initiation.

Questions & Answers

simple definition for respiratory system
Gift Reply
Respiratory system is a network of organs and tissues that helps you to breathe or help in getting the rids of oxygen and discharge of carbon dioxide in the body.
Ruhiyatu
how is a aerenchyma tissue adapted to its function
fatuma Reply
what does DNA mean
innocent Reply
dioxiribo nucleic acid
Lekan
what is a zygote
Victor Reply
zygote is developed or fertilized egg cell
Lekan
what is the difference between cell wall and cell membrane
Ruhiyatu Reply
cell wall is found in plant while cell membrane is found in animal cell
Lekan
please this is the main answer to that question okay Cell wall gives shape and support to the cell whiles Cell membrane support the movement of substances into and out of the cell. This question is very tricky that's why I asked.
Ruhiyatu
how cell I form
Elijah Reply
what difference between animal cell and plant cell
Lazarus Reply
what is animal call
Rita
Animal cell does not have a cell wall but plant cell have a cell wall
Ruhiyatu
plant have cell Wall well animal have not cell wall
Yula
what is fertilization?
Muhamed Reply
Fertilization is the fusion of male sex cell and female sex cell to form a zygote.
Ruhiyatu
What kind of nutrients is composed of plants
Annie Reply
phosphorus,potassium,nitrogen
Kritika
NPK
Ruhiyatu
what is hormones
Igwe Reply
hormon is the chemical messanger
Sneha
Genes can make someone dull?
Taperah
21ecological instrument and their diagrams
Ayomide Reply
cell biology
Muhamed
I am sorry
onuoha
for wat
ezeadaugo
no reason
KP
nothing but speculate
KP
Sorry without reason is nothing but speculate
Leilah
what are the kidney disease
Immaculate Reply
kidney stones
Gracelyne
it is a disease that affects the kidney
Miriam
what are some lung diseases
Gracelyne
kidney cancer
Victor
what is micro-organism
Jackson Reply
what is the hypothesis
Jackson
hypothesis is a proposed explanation for a phenomenon
Miriam
hypothesis is raw materials
KP
what is biology
KP
biology is the study of living things and their interaction with their environment
Miriam
what is zyogot?
Muhamed
what is fertilization?
Muhamed
zygote is an unfertilized eggs
KP
fertilization refers to the fusion of a sperm and ovum
KP
organs that can't be seen physically
Victor
what does mean stigma
Amira Reply
the stigma receives pollen grains during pollination
Ruhiyatu
what is the full of the MOST dangerous disease in the world where one stops sleeping and just dies :Hint ; FFI
God Reply
fatal familial insomnia which affects the thalamus
Miriam
there are other dangerous diseases like CAD i.e coronary artery disease
Miriam

Get the best Biology course in your pocket!





Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Biology' conversation and receive update notifications?

Ask