Pseudourine formation in small nuclear RNAs

Recent in vitro studies on the formation of pseudouridine (Ψ) in the spliceosomal small nuclear RNAs (snRNA) are reviewed. Multiple Ψ synthase activities, in some cases more that one per snRNA, are responsible for this modification of uridine. There is a requirement for Sm protein binding for the efficient formation of Ψ in U5 RNA but not for the modification of U2 RNA. The inhibition of Ψ formation by the incorporation of 5-fluorouridine in the snRNA is also reviewed.