RNA editing ( German: RNA editing ) is a biochemical process within certain cells or cell organelles, which can take place after transcription and prior to translation in the course of gene expression. The term describes the modification of individual nucleobases of the messenger RNA, after which no longer match the nucleotide sequence of the transcript of the nucleotide sequence of the original genomic DNA. Adjacent to the splicing, the RNA Edition illustrates another important form of post-transcriptional modification ( RNA processing ), resulting in the increase in the diversity of the transcriptome and thus, inter alia, to a significantly higher protein diversity.
In principle, a distinction between the insertion / deletion editing, inserted in which one or more nucleotides in the RNA or are removed from the RNA, and chemically modifying the individual nucleobases or riboses, for example, the deaminating of adenosine to inosine or the conversion of uridine to pseudouridine (which is more specifically referred to as RNA modification).
RNA editing in trypanosomes
Insertion and deletion editing occurs widely in mitochondria of trypanosomes on ( organisms, are also characterized by a more unusual form of RNA processing, the trans-splicing ). Almost every second uracil nucleotide of mitochondrial mRNAs is inserted with the aid of the so-called " Editosoms " in the primary transcript. Guide RNAs play an important role, they ensure specificity of the Editosoms and for inserting the correct number of Us ( cf. snoRNAs that serve a similar function).
RNA editing in higher eukaryotes
In higher eukaryotes such as mammals there is, however, almost exclusively, the chemical modification of single nucleotides. In many cases, proteins and complexes of snoRNAs provide ( the snoRNPs ) and related scaRNPs for the conversion of uridine to pseudouridine and the 2'-OH methylation riboses (eg ribosomal RNAs and snRNAs ) - this process is called RNA modification called. Much more widespread however is the direct enzymatic modification of bases without the aid of guide RNAs. Especially adenosine deaminases ( ADAR: Adenosine deaminase acting on RNA) deamination in the human transcriptome, a large number of adenosine residues to inosine ( which behaves in the base-pairing, such as guanosine ) and thus change the information from - according to recent figures - thousands of transcripts with far-reaching consequences for splicing, RNA stability and translation.
A well-studied example of RNA Edition still represents the apoB mRNA, in which there is a tissue-specific C to U editing ( deamination ). In edited RNA produced as a stop codon, resulting in the translation of a truncated isoform of the apolipoprotein B. The responsible catalytic peptide ( APOBEC ) is the most prominent representatives of the same protein family, which also includes the activation- induced cytidine deaminases (AID). An example of this and the serotonin 5-HT2C receptor, which adapt to its specificity to G- proteins, and affect different signaling pathways can result in the. Also, a large number of brain- specific transcripts is one of the objectives of the editing machinery ( potassium channel Kv1.1, glutamate receptor, etc.).
Another important function of the RNA only editing is to suppress the retrotransposition mainly of aluminum members and the defense of RNA viruses or DNA viruses with genomic RNA intermediate (for example, HIV - RNA and the pregenomic RNA of Hepatitis B virus). Also the diversity of antibodies is increased above the RNA editing.
RNA editing in plant
Between 20 and 40 nucleotides in plastids of seed plants do not agree with the genome - in each of these cases is a C to U editing instead. In the mitochondria of higher terrestrial plants, these changes are far more pronounced, there are not a gene is not affected by this modification, and the proportion of the modified nucleotides may be up to 20 percent of the gene. In lower plants ( algae to liverworts ) RNA Edition does not occur.
Diseases caused by disruption of RNA editing
Interference of RNA editing apparatus probably contribute also to various human diseases. This has been suggested, for example, amyotrophic lateral sclerosis (ALS) and in certain forms of epilepsy, schizophrenia and other neurological conditions.