Epitranscriptomics describes an aspect of molecular genetics, or a study thereof, that depends on biochemical modifications of RNA. By analogy to the term epigenetics, described as "functionally relevant changes to the genome that do not involve a change in the nucleotide sequence", epitranscriptomics can be defined as a functionally relevant changes to the transcriptome that do not involve a change in the ribonucleotide sequence. The epitranscriptome, therefore, is defined as the ensemble of such functionally relevant changes.
There are several types of RNA modifications that impact gene expression. These modifications happen to all types of cellular RNA including, but not limited to, ribosomal RNA(rRNA), transfer RNA (tRNA), messenger RNA (mRNA), and small nuclear RNA (snRNA). There are more than one hundred documented RNA modifications. A database maintained by the University of Albany details each modification. The most common and well-understood mRNA modification at present is the N6-Methyladenosine (m6A), which has been observed to occur an average of three times in every mRNA molecule.
The relative youth of this field means there is still much progress to be made in characterizing all modifications to the transcriptome and elucidating their mechanisms of action. Once these questions are answered and biologists have a better sense of the amount of variation in RNA modification, the focus will turn to each modification’s biological function. This has already been investigated in a select few proteins such as adenosine deaminase, which acts on RNA (ADAR). ADAR has been shown to affect antibody production and the innate immune system as well as transcripts encoding important receptors for the central nervous system. This plurality in function has caused some scientists to speculate that the epitransciptome may be even more expansive than the better defined epigenome.