In molecular biology, the small nucleolar RNA SNORA73 (also called U17/E1 RNA) belongs to the H/ACA class of small nucleolar RNAs (snoRNAs). Vertebrate U17 is intron-encoded and ranges in length from 200-230 nucleotides, longer than most snoRNAs. It is one of the most abundant snoRNAs in human cells and is essential for the cleavage of pre-rRNA within the 5' external transcribed spacer (ETS). This cleavage leads to the formation of 18S rRNA. Regions of the U17 RNA are complementary to rRNA and act as guides for RNA/RNA interactions, although these regions do not seem to be well conserved between organisms.
^Cervelli M, Cecconi F, Giorgi M, Annesi F, Oliverio M, Mariottini P (February 2002). "Comparative structure analysis of vertebrate U17 small nucleolar RNA (snoRNA)". Journal of Molecular Evolution. 54 (2): 166–79. doi:10.1007/s00239-001-0065-2. PMID11821910.