Within the field of molecular biology, the epitranscriptome includes all the biochemical modifications of the RNA (the transcriptome) within a cell. In analogy to epigenetics that describes "functionally relevant changes to the genome that do not involve a change in the nucleotide sequence", epitranscriptomics involves all functionally relevant changes to the transcriptome that do not involve a change in the ribonucleotide sequence. Thus, the epitranscriptome can be defined as the ensemble of such functionally relevant changes.
There are several types of RNA modifications that impact gene expression. These modifications happen to many types of cellular RNA including, but not limited to, ribosomal RNA (rRNA), transfer RNA (tRNA), messenger RNA (mRNA), and small nuclear RNA (snRNA). The most common and well-understood mRNA modification at present is N-Methyladenosine (mA), which has been observed to occur an average of three times in every mRNA molecule.
Currently, work is focused on determining the types of and location of RNA modifications, determining if these modification have function, and if so, what is their mechanism of action. Similar to the epigenome, the epitranscriptome has "writers" and "erasers" that mark RNA and "readers" that translate those marks into function. One function that has been elucidated involves the enzyme adenosine deaminase (ADAR), which acts on RNA. ADAR affects a series of cellular processes, including alternative splicing, microRNAs, the innate immune system, and leads to protein recoding especially for important receptors in the central nervous system.