he genes that encode the miRNA are also named using the same three-letter prefix, with capitalization, hyphenation, and italics according to the conventions of the organism (for example,
mir-1 in
C. elegans and
Drosophila, MIR156 in
Arabidopsis and rice). The identifying numbers are assigned sequentially, with identical miRNAs having the same number, regardless of organism. Nearly identical orthologs can also be given the same number, at the discretion of the researcher. For example, miR-1 of
Drosophila differs by a single nucleotide from miR-1 of
C. elegans and humans. Identical or very similar miRNA sequences within a species can also be given the same number, with their genes distinguished by letter and/or numeral suffixes, according to the convention of the organism (e.g., the ∼22-nt transcripts of
Drosophila mir-13a and
mir-13b are slightly different in sequence, whereas those of
mir-6-
1 and
mir-6-
2 are identical;
Lagos-Quintana et al. 2001).