Z18 small nucleolar RNA is a non-coding RNA

Non-coding RNA

A non-coding RNA is a functional RNA molecule that is not translated into a protein. Less-frequently used synonyms are non-protein-coding RNA , non-messenger RNA and functional RNA . The term small RNA is often used for short bacterial ncRNAs...

 (ncRNA) molecule which functions in the modification of other small nuclear RNA

Small nuclear RNA

Small nuclear ribonucleic acid is a class of small RNA molecules that are found within the nucleus of eukaryotic cells. They are transcribed by RNA polymerase II or RNA polymerase III and are involved in a variety of important processes such as RNA splicing , regulation of transcription factors ...

s (snRNAs). This type of modifiying RNA is usually located in the nucleolus

Nucleolus

The nucleolus is a non-membrane bound structure composed of proteins and nucleic acids found within the nucleus. Ribosomal RNA is transcribed and assembled within the nucleolus...

 of the eukaryotic cell which is a major site of snRNA biogenesis. It is known as a small nucleolar RNA

SnoRNA

Small nucleolar RNAs are a class of small RNA molecules that primarily guide chemical modifications of other RNAs, mainly ribosomal RNAs, transfer RNAs and small nuclear RNAs...

 (snoRNA) and also often referred to as a guide RNA.
Z18 snoRNA belongs to the C/D box class of snoRNAs which contain the conserved sequence motifs known as the C box (UGAUGA) and the D box (CUGA). Most of the members of the box C/D family function in directing site-specific 2'-O-methylation

Methylation

In the chemical sciences, methylation denotes the addition of a methyl group to a substrate or the substitution of an atom or group by a methyl group. Methylation is a form of alkylation with, to be specific, a methyl group, rather than a larger carbon chain, replacing a hydrogen atom...

of substrate RNAs.