Publish Your Research Online
Get Recognition - International Audience
Request for an Author Account | Login | Submit Article
|HOME||FAQ||TOP AUTHORS||FORUMS||PUBLISH ARTICLE|
RNA Editing - Mechanisms, Features and SignificanceBY: Dr. Suresh Kaushik | Category: DNA | Submitted: 2013-03-07 12:03:08
Article Summary: "The information flows directly from DNA to protein through the RNA intermediate molecule. But, it has been discovered that the information that is contained in the DNA is not always found in the RNA products used to make proteins. Mitochondria and chloroplast contain the biochemical machinery to alter the sequence of the final t.."
The central dogma of molecular genetics states that the information that is found in DNA is used to produce mRNA molecules that are instrumental in the production of proteins. Therefore, the information flows directly from DNA to protein through the RNA intermediate molecule. But, it has been discovered that the information that is contained in the DNA is not always found in the RNA products used to make proteins. Mitochondria and chloroplast contain the biochemical machinery to alter the sequence of the final transcription product. This process is called RNA editing. Such changes have been observed in tRNA, rRNA and mRNA molecules of eukaryotes, but not prokaryotes. RNA editing occurs in the cell nucleus, cytosol, as well as in mitochondria and plastids.The diversity of RNA editing mechanisms includes nucleoside modifications such as C to U and A to I deaminations, as well as non-template nucleotide additions and insertions. RNA editing in mRNAs effectively alters the amino acid sequence of the encoded protein so that it differs from that predicted by the genomic DNA sequence.
There are mainly two mechanisms for RNA editing:
• Substitution Editing: chemical alteration of individual nucleotides. These alterations are catalyzed by enzymes that recognize a specific target sequence of nucleotides e.g. cytidine deaminases that convert a C in the RNA to uracil (U) and adenosine deaminases that convert an A to inosine (I), which the ribosome translates as a G. So, a CAG codon (for Gln) can be converted to a CGG codon (for Arg).
• Insertion/Deletion Editing: insertion or deletion of nucleotides in the RNA. These alterations are mediated by guide RNA (gRNA) molecules that base-pair with the RNA to be edited and serve as a template for the addition (or removal) of nucleotides in the target
Sequence analysis of a number of cytochrome c oxidase subunit II genes from non-plant species revealed that a tryptophan residue was invariant at several locations in the final protein product. But sequence analysis of this gene in several plant species revealed arginine at those positions. This amino acid change would cause a radical alteration in protein structure because an acidic amino acid would replace a neutral, hydrophobic amino acid.
Since a single base pair change in the codons for the two amino acids could generate this change (CGG for UGG), it was suggested that CGG encoded for tryptophan and not arginine in plant mitochondria. But this change in codon usage was not universal, that is some CGG codons actually specified arginine in the final protein product.
By sequencing the mRNA products for cytochrome c oxidase subunit II genes, it was found that in the mRNA the cytosine residue had been changed (edited) to uridine at the sequence location where the invariant tryptophan residue is found. This changed the codon at that location to UGG which is recognized by a tRNA that carries the amino acid tryptophan. An analysis of three other plant mitochondrial genes where the same altered codon usage was predicted suggested that mRNA editing was also occurring at the codon and that a cytosine residue was edited to uridine.
Some important features are:
• Editing can occur in both mitochondria and chloroplasts
• Plant mitochondria do not use the universal genetic code.
• The RNA editing events occur at random in the transcript.
• Both 5' and 3' non-coding regions of mRNAs may undergo editing.
• Structural RNAs such as tRNAs and rRNAs are also affected.
• Editing can convert a tryptophan codon to a arginine codon (CGG to UGG).
• Start AUG codon can be created from threonine codon (ACG)
• Stop codons can be created by editing CAG, CAA and CGA codons.
• The most frequent amino acid substations derived from RNA editing are Pro to Leu, Ser to Leu and Ser to Phe.
The primary benefit of RNA editing could be evolutionary conservation of protein structure. For example, bound copper is required for the funciton of cytochrome c oxidase subunit II (coxII). After editing, all amino acids at the number 228 position are converted to cysteine, an amino acid required for copper (Cu) to bind. In all species except for plants, the coxII gene encodes for methionine at codon number 235. In plants, this methionine is generated by RNA editing. These events suggest that this protein is under very strong structural and functional constraints.
About Author / Additional Info:
Comments on this article: (0 comments so far)
• Seed Storage Proteins
• Environmental Pollution - List of Most Common Pollutants
• Microalgae Uses in Human Nutrition: For Making Biodiesel and Colorant
• Common Feed Additives in Animal Nutrition
Latest Articles in "DNA" category:
• Identifying a Specific Clone in CDNA and Genomic Library
• Biotechnolgical Techniques For DNA Analysis
• DNA Extraction:Procedure and Importance in Forensics
• Chromosomal Aberrations and its Types
• Gene Knockout in Mice
• DNA Repair Types: Excision, Postreplication, Recombination and Lesion Removal
• Microarrays and Gene Expressions - Principle and Procedure
• Human Cytogenetics - Karyotype
• Experimental Issues in Microarrays
• Nuclear pre-mRna Splicing: The Story of Introns and Exons
• Chain Termination Method: A Generic Method For DNA Sequencing
• Transposable Elements - The Story of Jumping Genes
• RNA Interference - The Art of Gene Silencing
• Protein Biosynthesis: Decoding the Code (Part-1)
• Protein Biosynthesis: Decoding the Code (Part - 2)
• Mutagenesis - Types and Uses
• C-Value, An Unsolved Paradox?
• Mechanism of Epigenetics
• Techniques of Epigenetic Studies
Important Disclaimer: All articles on this website are for general information only and is not a professional or experts advice. We do not own any responsibility for correctness or authenticity of the information presented in this article, or any loss or injury resulting from it. We do not endorse these articles, we are neither affiliated with the authors of these articles nor responsible for their content. Please see our disclaimer section for complete terms.
Copyright © 2010 biotecharticles.com - Do not copy articles from this website.
ARTICLE CATEGORIES :
| Disclaimer/Privacy/TOS | Submission Guidelines | Contact Us