Question: Where are RNA Nucleotides found?
About the article "RNA", section "In RNA processing".

Candidate passages:
The ryfA RNA gene is a non-coding RNA present in "E. coli", "Shigella flexneri" and "Salmonella" species where it is found between the "ydaN" and "dbpA" genes.
These RNA genes are about 300 nucleotides in length.
The function of this RNA is unknown. 
1986–2000.RNA sequences can be edited within cells.
Messenger RNA precursors from a wide range of organisms can be edited before being translated into protein.
In this process, non-encoded nucleotides may be inserted into specific sites in the RNA, and encoded nucleotides may be removed or replaced.
RNA editing was first discovered within the mitochondria of kinetoplastid protozoans, where it has been shown to be extensive.
For example, some protein-coding genes encode fewer than 50% of the nucleotides found within the mature, translated mRNA.
Other RNA editing events are found in mammals, plants, bacteria and viruses.
These latter editing events involve fewer nucleotide modifications, insertions and deletions than the events within kinetoplast DNA, but still have high biological significance for gene expression and its regulation. 
Many RNAs are involved in modifying other RNAs.
Introns are spliced out of pre-mRNA by spliceosomes, which contain several small nuclear RNAs (snRNA), or the introns can be ribozymes that are spliced by themselves.RNA can also be altered by having its nucleotides modified to other nucleotides than A, C, G and U.
In eukaryotes, modifications of RNA nucleotides are in general directed by small nucleolar RNAs (snoRNA; 60-300 nt), found in the nucleolus and cajal bodies.
snoRNAs associate with enzymes and guide them to a spot on an RNA by basepairing to that RNA.
These enzymes then perform the nucleotide modification.
rRNAs and tRNAs are extensively modified, but snRNAs and mRNAs can also be the target of base modification.
RNA can also be methylated.
RNA replication is the copying of one RNA to another.
Many viruses replicate this way.
The enzymes that copy RNA to new RNA, called RNA-dependent RNA polymerases, are also found in many eukaryotes where they are involved in RNA silencing.
RNA editing, in which an RNA sequence is altered by a complex of proteins and a "guide RNA", could also be considered an RNA-to-RNA transfer. 
 "For further information, see RNA and Messenger RNA" Background on RNA.RNAs are a type of large biological molecules, whose individual building blocks are called nucleotides.
The name "poly(A) tail" (for polyadenylic acid tail) reflects the way RNA nucleotides are abbreviated, with a letter for the base the nucleotide contains (A for adenine, C for cytosine, G for guanine and U for uracil).
RNAs are produced ("transcribed") from a DNA template.
By convention, RNA sequences are written in a 5' to 3' direction.
The 5' end is the part of the RNA molecule that is transcribed first, and the 3' end is transcribed last.
The 3' end is also where the poly(A) tail is found on polyadenylated RNAs.
Messenger RNA (mRNA) is RNA that has a coding region that acts as a template for protein synthesis ("translation").
The rest of the mRNA, the "untranslated regions", tune how active the mRNA is.
There are also many RNAs that are not translated, called non-coding RNAs.
Like the untranslated regions, many of these non-coding RNAs have regulatory roles.