The ribosomal 5.8S RNA: eukaryotic adaptation or processing variant?

A striking difference between the cytoplasmic ribosomes of eukaryotes and prokaryotes is the presence (in eukaryotes) of one additional RNA component, the 5.8S rRNA. This RNA, which is hydrogen bonded to the cognate high molecular weight RNA of the large subunit, is about 160 nucleotides in length, and is cotranscribed with the high molecular weight rRNA as part of a much larger precursor molecule, the nucleolar 36S-45S rRNA. Because of its relatively small size the 5.8S RNA is considered a good model for studies on rRNA structure, synthesis, maturation, ribosomal integration, function, and even evolution. Over the last decade numerous studies have examined these questions with many interesting results, including the probability that this RNA sequence may actually be present in all ribosomes, although not necessarily as a separate RNA component. Their findings are summarized in this review.