Eukaryotic transcription
Encyclopedia
Eukaryotic transcription is more complex than prokaryotic transcription
. For instance, in eukaryotes the genetic material (DNA), and therefore transcription, is primarily localized to the nucleus
, where it is separated from the cytoplasm
(in which translation occurs) by the nuclear membrane. DNA is also present in mitochondria in the cytoplasm
and mitochondria utilize a specialized RNA polymerase for transcription. This allows for the temporal regulation of gene expression through the sequestration of the RNA in the nucleus, and allows for selective transport of RNAs to the cytoplasm
, where the ribosome
s reside.
The basal eukaryotic transcription complex includes the RNA polymerase and additional proteins that are necessary for correct initiation and elongation.
, the highly conserved DNA recognition sequence for the TATA box binding protein, TBP
, whose binding initiates transcription complex assembly at the promoter.
Some genes also have enhancer
elements that can be thousands of bases upstream or downstream of the transcription initiation site. Combinations of these upstream control elements and enhancers regulate and amplify the formation of the basal transcription complex.
There are many eukaryotes that differ from the canonical presentation of the roles of RNA polymerasespossess four distinct RNA polymerases. Other organisms utilize RNA polymerase I to transcribe certain protein-coding genes in addition to rRNAs.
is achieved through the interaction of several levels of control including the regulation of transcription initiation. Most (not all) eukaryotes possess robust methods of regulating transcription initiation on a gene-by-gene basis. The transcription of a gene can be regulated by cis-acting elements within the regulatory regions of the DNA, and trans-acting factors that include transcription factor
s and the basal transcription complex.
Prokaryotic transcription
Prokaryotic transcription is the process in which messenger RNA transcripts of genetic material in prokaryotes are produced, to be translated for the production of proteins. Prokaryotic transcription occurs in the cytoplasm alongside translation. Unlike in eukaryotes, prokaryotic transcription and...
. For instance, in eukaryotes the genetic material (DNA), and therefore transcription, is primarily localized to the nucleus
Cell nucleus
In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The genes within these...
, where it is separated from the cytoplasm
Cytoplasm
The cytoplasm is a small gel-like substance residing between the cell membrane holding all the cell's internal sub-structures , except for the nucleus. All the contents of the cells of prokaryote organisms are contained within the cytoplasm...
(in which translation occurs) by the nuclear membrane. DNA is also present in mitochondria in the cytoplasm
Cytoplasm
The cytoplasm is a small gel-like substance residing between the cell membrane holding all the cell's internal sub-structures , except for the nucleus. All the contents of the cells of prokaryote organisms are contained within the cytoplasm...
and mitochondria utilize a specialized RNA polymerase for transcription. This allows for the temporal regulation of gene expression through the sequestration of the RNA in the nucleus, and allows for selective transport of RNAs to the cytoplasm
Cytoplasm
The cytoplasm is a small gel-like substance residing between the cell membrane holding all the cell's internal sub-structures , except for the nucleus. All the contents of the cells of prokaryote organisms are contained within the cytoplasm...
, where the ribosome
Ribosome
A ribosome is a component of cells that assembles the twenty specific amino acid molecules to form the particular protein molecule determined by the nucleotide sequence of an RNA molecule....
s reside.
The basal eukaryotic transcription complex includes the RNA polymerase and additional proteins that are necessary for correct initiation and elongation.
Initiation
Among eukaryotes that regulate the transcription of individual genes, the core promoter of protein-encoding gene contains binding sites for the basal transcription complex and RNA polymerase II, and is normally within about 50 bases upstream of the transcription initiation site. Further transcriptional regulation is provided by upstream control elements (UCEs), usually present within about 200 bases upstream of the initiation site. The core promoter for Pol II sometimes contains a TATA boxTATA box
The TATA box is a DNA sequence found in the promoter region of genes in archaea and eukaryotes; approximately 24% of human genes contain a TATA box within the core promoter....
, the highly conserved DNA recognition sequence for the TATA box binding protein, TBP
TATA Binding Protein
The TATA-binding protein is a general transcription factor that binds specifically to a DNA sequence called the TATA box. This DNA sequence is found about 35 base pairs upstream of the transcription start site in some eukaryotic gene promoters...
, whose binding initiates transcription complex assembly at the promoter.
Some genes also have enhancer
Enhancer (genetics)
In genetics, an enhancer is a short region of DNA that can be bound with proteins to enhance transcription levels of genes in a gene cluster...
elements that can be thousands of bases upstream or downstream of the transcription initiation site. Combinations of these upstream control elements and enhancers regulate and amplify the formation of the basal transcription complex.
Transcription process
Eukaryotes have three nuclear RNA polymerases, each with distinct roles and properties:| Name | >- | nucleolus Nucleolus The nucleolus is a non-membrane bound structure composed of proteins and nucleic acids found within the nucleus. Ribosomal RNA is transcribed and assembled within the nucleolus... |
>- | nucleus | messenger RNA (mRNA) and most small nuclear RNAs (snRNAs) |- | RNA Polymerase III RNA polymerase III RNA polymerase III transcribes DNA to synthesize ribosomal 5S rRNA, tRNA and other small RNAs. The genes transcribed by RNA Pol III fall in the category of "housekeeping" genes whose expression is required in all cell types and most environmental conditions... (Pol III, Pol C) |
nucleus (and possibly the nucleolus Nucleolus The nucleolus is a non-membrane bound structure composed of proteins and nucleic acids found within the nucleus. Ribosomal RNA is transcribed and assembled within the nucleolus... -nucleoplasm Nucleoplasm Similar to the cytoplasm of a cell, the nucleus contains nucleoplasm or karyoplasm. The nucleoplasm is one of the types of protoplasm, and it is enveloped by the nuclear membrane or nuclear envelope. The nucleoplasm is a highly viscous liquid that surrounds the chromosomes and nucleoli... interface) |
transfer RNA (tRNA) and other small RNAs (including the small 5S rRNA) |
There are many eukaryotes that differ from the canonical presentation of the roles of RNA polymerasespossess four distinct RNA polymerases. Other organisms utilize RNA polymerase I to transcribe certain protein-coding genes in addition to rRNAs.
Transcription regulation
The regulation of gene expressionRegulation of gene expression
Gene modulation redirects here. For information on therapeutic regulation of gene expression, see therapeutic gene modulation.Regulation of gene expression includes the processes that cells and viruses use to regulate the way that the information in genes is turned into gene products...
is achieved through the interaction of several levels of control including the regulation of transcription initiation. Most (not all) eukaryotes possess robust methods of regulating transcription initiation on a gene-by-gene basis. The transcription of a gene can be regulated by cis-acting elements within the regulatory regions of the DNA, and trans-acting factors that include transcription factor
Transcription factor
In molecular biology and genetics, a transcription factor is a protein that binds to specific DNA sequences, thereby controlling the flow of genetic information from DNA to mRNA...
s and the basal transcription complex.