Table 1.

Brief summary of RNA biotypes with known roles in molecular biology and addiction.

Type of RNA	Description	Biological function
mRNA	Messenger RNA (e.g., Bdnf)	Translation into proteins
tRNA	Transfer RNA	Regulation of protein translation
rRNA	Ribosomal RNA	Protein synthesis
snoRNA	Small nucleolar RNA	Chemical modification of tRNA and rRNA
snRNA	Small nuclear RNA	Processing of pre-mRNA
siRNA	Small interfering RNA	Double-stranded RNA regulation of mRNA degradation
piRNA	Piwi-interacting RNA	Post-transcriptional regulation of RNA silencing
miRNA	MicroRNA (e.g., miR-9)	Anti-sense sequence complementarity regulation of gene expression
circRNA	Circular RNA (fused 3′-UTR and 5′-UTR ends, e.g., circ_1639)	Anti-sense sequence regulation of microRNAs
lncRNA	Long non-coding RNA (e.g., MALAT1)	Binding and regulation of DNA, RNA, and protein

Less than 2% of the genome consists of protein-coding (mRNA) genes. A significant fraction of transcribed sequences from the mammalian genome are represented by a diverse set of non-coding genes: tRNA, rRNA, snoRNA, snRNA, siRNA, piRNA, miRNA, circRNA, and lncRNA. Each of class of these non-coding RNAs participates in discrete biochemical functions and may have significant roles in addiction to alcohol and other substances of abuse.