Editing RNA (section)

===Synthesis===
Synthesis of RNA typically occurs in the cell nucleus and is usually catalyzed by an enzyme—[[RNA polymerase]]—using DNA as a template, a process known as [[Transcription (genetics)|transcription]]. Initiation of transcription begins with the binding of the enzyme to a [[promoter (biology)|promoter]] sequence in the DNA (usually found "upstream" of a gene). The DNA double helix is unwound by the [[helicase]] activity of the enzyme. The enzyme then progresses along the template strand in the 3’ to 5’ direction, synthesizing a complementary RNA molecule with elongation occurring in the 5’ to 3’ direction. The DNA sequence also dictates where termination of RNA synthesis will occur.<ref>{{cite journal | vauthors = Nudler E, Gottesman ME | title = Transcription termination and anti-termination in E. coli | journal = Genes to Cells | volume = 7 | issue = 8 | pages = 755–68 | date = August 2002 | pmid = 12167155 | doi = 10.1046/j.1365-2443.2002.00563.x | s2cid = 23191624 | doi-access =  }}</ref>

[[Primary transcript]] RNAs are often [[Post-transcriptional modification|modified]] by enzymes after transcription. For example, a [[poly(A) tail]] and a [[5' cap]] are added to eukaryotic [[pre-mRNA]] and [[intron]]s are removed by the [[spliceosome]].

There are also a number of [[RNA-dependent RNA polymerase]]s that use RNA as their template for synthesis of a new strand of RNA. For instance, a number of [[Orthornavirae|RNA viruses]] (such as poliovirus) use this type of enzyme to replicate their genetic material.<ref>{{cite journal | vauthors = Hansen JL, Long AM, Schultz SC | title = Structure of the RNA-dependent RNA polymerase of poliovirus | journal = Structure | volume = 5 | issue = 8 | pages = 1109–22 | date = August 1997 | pmid = 9309225 | doi = 10.1016/S0969-2126(97)00261-X | doi-access = free }}</ref> Also, RNA-dependent RNA polymerase is part of the [[RNA interference]] pathway in many organisms.<ref>{{cite journal | vauthors = Ahlquist P | title = RNA-dependent RNA polymerases, viruses, and RNA silencing | journal = Science | volume = 296 | issue = 5571 | pages = 1270–73 | date = May 2002 | pmid = 12016304 | doi = 10.1126/science.1069132 | bibcode = 2002Sci...296.1270A | s2cid = 42526536 }}</ref>