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Post-transcriptional modification

 

 
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Post-transcriptional modification
 
 
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Post-transcriptional modification is a process in cell biology
Cell biology

Cell biology is an list of academic disciplines that studies cell s ? their physiology properties, their structure, the organelles they contain, interactions with their environment, their cell cycle, cell division and apoptosis....
 by which, in eukaryotic cells, primary transcript RNA
RNA

Ribonucleic acid is a type of molecule that consists of a long chain of nucleotide units. Each nucleotide consists of a nucleobase, a ribose sugar, and a phosphate....
 is converted into mature RNA
RNA

Ribonucleic acid is a type of molecule that consists of a long chain of nucleotide units. Each nucleotide consists of a nucleobase, a ribose sugar, and a phosphate....
. A notable example is the conversion of precursor messenger RNA into mature
Mature messenger RNA

Mature messenger RNA, often abbreviated as mature mRNA is a eukaryotic RNA transcript that has been Splicing and mRNA and is ready for translation in the course of protein synthesis....
 messenger RNA
Messenger RNA

Messenger ribonucleic acid is a molecule of RNA encoding a chemical "blueprint" for a protein product. mRNA is transcription from a DNA template, and carries coding information to the sites of protein synthesis: the ribosomes....
 (mRNA), which includes splicing
Splicing (genetics)

In molecular biology, splicing is a modification of an RNA after transcription , in which introns are removed and exons are joined. This is needed for the typical eukaryotic messenger RNA before it can be used to produce a correct protein through translation ....
 and occurs prior to protein synthesis
Protein synthesis

Protein synthesis is the creation of proteins using DNA and RNA. Proteins can often be synthesized directly from genes by Translation mRNA. When a protein is harmful and needs to be available on short notice or in large quantities, a protein precursor is produced....
. This process is vital for the correct translation
Translation

Translation is the hermeneutics of the Meaning of a text and the subsequent production of an Dynamic and formal equivalence text, likewise called a "translation," that communicates the same message in another language....
 of the genome
Genome

In classical genetics, the genome of a diploid organism including eukarya refers to a full set of chromosomes or genes in a gamete; thereby, a regular somatic cell contains two full sets of genomes....
s of eukaryotes as the human primary RNA transcript that is produced as a result of transcription contains both exons, which are coding sections of the primary RNA transcript and introns, which are the non coding sections of the primary RNA transcript.

pre-mRNA molecule undergoes three main modifications.






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Post-transcriptional modification is a process in cell biology
Cell biology

Cell biology is an list of academic disciplines that studies cell s ? their physiology properties, their structure, the organelles they contain, interactions with their environment, their cell cycle, cell division and apoptosis....
 by which, in eukaryotic cells, primary transcript RNA
RNA

Ribonucleic acid is a type of molecule that consists of a long chain of nucleotide units. Each nucleotide consists of a nucleobase, a ribose sugar, and a phosphate....
 is converted into mature RNA
RNA

Ribonucleic acid is a type of molecule that consists of a long chain of nucleotide units. Each nucleotide consists of a nucleobase, a ribose sugar, and a phosphate....
. A notable example is the conversion of precursor messenger RNA into mature
Mature messenger RNA

Mature messenger RNA, often abbreviated as mature mRNA is a eukaryotic RNA transcript that has been Splicing and mRNA and is ready for translation in the course of protein synthesis....
 messenger RNA
Messenger RNA

Messenger ribonucleic acid is a molecule of RNA encoding a chemical "blueprint" for a protein product. mRNA is transcription from a DNA template, and carries coding information to the sites of protein synthesis: the ribosomes....
 (mRNA), which includes splicing
Splicing (genetics)

In molecular biology, splicing is a modification of an RNA after transcription , in which introns are removed and exons are joined. This is needed for the typical eukaryotic messenger RNA before it can be used to produce a correct protein through translation ....
 and occurs prior to protein synthesis
Protein synthesis

Protein synthesis is the creation of proteins using DNA and RNA. Proteins can often be synthesized directly from genes by Translation mRNA. When a protein is harmful and needs to be available on short notice or in large quantities, a protein precursor is produced....
. This process is vital for the correct translation
Translation

Translation is the hermeneutics of the Meaning of a text and the subsequent production of an Dynamic and formal equivalence text, likewise called a "translation," that communicates the same message in another language....
 of the genome
Genome

In classical genetics, the genome of a diploid organism including eukarya refers to a full set of chromosomes or genes in a gamete; thereby, a regular somatic cell contains two full sets of genomes....
s of eukaryotes as the human primary RNA transcript that is produced as a result of transcription contains both exons, which are coding sections of the primary RNA transcript and introns, which are the non coding sections of the primary RNA transcript.

mRNA processing

The pre-mRNA molecule undergoes three main modifications. These modifications are 5' cap
5' cap

The 5' cap is a specially altered nucleotide on the 5' end of precursor messenger RNA and some other primary RNA transcripts as found in eukaryotes and, as a special exception, caliciviruses such as norovirus....
ping, 3' polyadenylation
Polyadenylation

Polyadenylation is the addition of a poly tail, a stretch of RNA where all the nucleobase are adenines, onto an RNA molecule. In eukaryotes, polyadenylation is part of the process that produces mature messenger RNA for translation ....
, and RNA splicing, which occur in the cell nucleus
Cell nucleus

In cell biology, the nucleus , also sometimes referred to as the "control center", is a membrane-enclosed organelle found in all eukaryote cell ....
 before the RNA is translated.

5' Processing


Capping
Capping of the pre-mRNA involves the addition of 7-methylguanosine (m7G) to the 5' end. In order to achieve this, the terminal 5' phosphate requires removal, which is done by the aid of a phosphatase
Phosphatase

A phosphatase is an enzyme that removes a phosphate group from its Substrate by Hydrolysis phosphoric acid monoesters into a phosphate ion and a molecule with a free hydroxyl group ....
 enzyme. The enzyme guanosyl transferase then catalyses the reaction which produces the diphosphate 5' end. The diphosphate 5' prime end then attacks the a phosphorus atom of a GTP
GTP

GTP may stand for:* Global Tower Partners, a private tower company based in the US* Guanosine triphosphate, an organic chemical* GPRS Tunnelling Protocol, for connecting over a network...
 molecule in order to add the guanine
Guanine

Guanine is one of the five main nucleobases found in the nucleic acids DNA and RNA, the others being adenine, cytosine, thymine, and uracil. In DNA, guanine is paired with cytosine....
  residue in a 5'5' triphosphate link. The enzyme S-adenosyl methionine
S-Adenosyl methionine

S-Adenosyl methionine is a coenzyme involved in methyl group transfers. SAM was first discovered in Italy by G. L. Cantoni in 1952. It is made from adenosine triphosphate and methionine by methionine adenosyltransferase ....
 then methylates the guanine ring at the N-7 position. This type of cap, with just the (m7G) in position is called a cap 0 structure. The ribose
Ribose

Ribose, primarily occurring as D-ribose, is an organic compound that occurs widely in nature. It is an aldopentose, that is a monosaccharide containing five carbon atoms that, in its acyclic form, has an aldehyde functional group at one end....
 of the adjacent nucleotide
Nucleotide

Nucleotides are molecules that comprise the structural units of RNA and DNA. Additionally, nucleotides play central roles in metabolism. In that capacity, they serve as sources of chemical energy , participate in cell signaling , and are incorporated into important cofactors of enzymatic reactions ....
 may also be methylated to give a cap 1. Methylation of nucleotides downstream of the RNA molecule produce cap 2, cap 3 structures and so on. In these cases the methyl groups are added to the 2' OH groups of the ribose sugar. The cap protects the 5' end of the primary RNA transcript from attack by ribonucleases that have specificity to the 3'5' phosphodiester bonds.

3' Processing


Cleavage and Polyadenylation

The pre-mRNA processing at the 3' end of the RNA molecule involves cleavage of its 3' end and then the addition of about 200 adenine
Adenine

Adenine is a nucleobase with a variety of roles in biochemistry including cellular respiration, in the form of both the energy-rich adenosine triphosphate and the cofactor s nicotinamide adenine dinucleotide and flavin adenine dinucleotide , and Protein biosynthesis, as a chemical component of DNA and RNA....
 residues to form a poly(A) tail. The cleavage and adenylation reactions occur if a polyadenylation signal sequence
Polyadenylation

Polyadenylation is the addition of a poly tail, a stretch of RNA where all the nucleobase are adenines, onto an RNA molecule. In eukaryotes, polyadenylation is part of the process that produces mature messenger RNA for translation ....
 (5'- AAUAAA-3') is located near the 3' end of the pre-mRNA molecule, which is followed by another sequence, which is usually (5'-CA-3'). The second signal is the site of cleavage. A GU-rich sequence is also usually present further downstream on the pre-mRNA molecule. After the synthesis of the sequence elements, two multisubunit protiens called cleavage and polyadenylation specificity factor
Cleavage and polyadenylation specificity factor

Cleavage and polyadenylation specificity factor is involved in the cleavage of the 3' signaling region from a newly synthesized pre-messenger RNA molecule in the process of transcription ....
 (CPSF) and cleavage stimulation factor
Cleavage stimulation factor

Cleavage stimulation factor is an RNA-binding protein.Genes, , External links...
 (CStF) are transferred from RNA Polymerase II
RNA polymerase II

RNA polymerase II is an enzyme found in eukaryotic cells. It catalyzes the Transcription of DNA to synthesize precursors of mRNA and most snRNA and microRNA....
 to the RNA molecule. The two factors bind to the sequence elements. A protein complex forms which contains additional cleavage factors and the enzyme Polyadenylate Polymerase (PAP). This complex cleaves the RNA between the polyadenylation sequence and the GU-rich sequence at the cleavage site marked by the (5'-CA-3') sequences. Poly(A) polymerase then adds about 200 adenine units to the new 3' end of the RNA molecule using ATP
ATP

ATP may refer to:...
 as a precursor. As the poly(A) tails is synthesised, it binds multiple copies of poly(A) binding protein, which protects the 3'end from ribonuclease digestion.

Splicing


RNA splicing is the process by which intron
Intron

Introns, derived from the term "intragenic regions" and also called intervening sequence , are DNA regions in a gene that are not translated into proteins....
s, regions of RNA that do not code for protein, are removed from the pre-mRNA and the remaining exon
Exon

An exon in a gene is a DNA or RNA sequence that is translated into RNA or protein. In contrast, an intron is a DNA sequence in the gene that is not translated....
s connected to re-form a single continuous molecule. Although most RNA splicing occurs after the complete synthesis and end-capping of the pre-mRNA, transcripts with many exons can be spliced co-transcriptionally. The splicing reaction is catalyzed by a large protein complex called the spliceosome
Spliceosome

A spliceosome is a complex of specialized RNA and protein subunits that removes introns from a Transcription pre-Messenger RNA segment. This process is generally referred to as splicing ....
 assembled from proteins and small nuclear RNA
Small nuclear RNA

Small nuclear RNA is a class of small RNA molecules that are found within the nucleus of eukaryotic cells. They are transcribed by RNA polymerase II or RNA polymerase III and are involved in a variety of important processes such as RNA splicing , regulation of transcription factors or RNA polymerase II , and maintaining the telomeres....
 molecules that recognize splice sites in the pre-mRNA sequence. Many pre-mRNAs, including those encoding antibodies
Antibody

Antibodies are gamma globulin proteins that are found in blood or other bodily fluids of vertebrates, and are used by the immune system to identify and neutralize foreign objects, such as bacterium and viruses....
, can be spliced in multiple ways to produce different mature mRNAs that encode different protein sequences
Primary structure

In biochemistry, the primary structure of a biological molecule is the exact specification of its atomic composition and the chemical bonds connecting those atoms ....
. This process is known as alternative splicing
Alternative splicing

Alternative splicing is the RNA splicing variation mechanism in which the exons of the primary gene transcript, the pre-mRNA, are separated and reconnected so as to produce alternative ribonucleotide arrangements....
, and allows production of a large variety of proteins from a limited amount of DNA.

Citations


See also

  • messenger RNA
    Messenger RNA

    Messenger ribonucleic acid is a molecule of RNA encoding a chemical "blueprint" for a protein product. mRNA is transcription from a DNA template, and carries coding information to the sites of protein synthesis: the ribosomes....
  • translation
    Translation (genetics)

    Translation is the first stage of protein biosynthesis . Translation is the production of proteins by decoding mRNA produced in Transcription ....
  • RNA editing
    RNA editing

    The term RNA editing describes those molecular processes in which the information content in an RNA molecule is altered through a chemical change in the base makeup....
  • RNA-Seq
    RNA-Seq

    RNA-Seq, also called "Whole Transcriptome Shotgun Sequencing" and dubbed "a revolutionary tool for transcriptomics" , refers to the use of High-throughput sequencing technologies to sequence cDNA in order to get information about a sample's RNA content, a technique that is quickly becoming invaluable in the study of diseases like cancer ....


External links