Pseudouridine formation in small nuclear RNAs.

Recent in vitro studies on the formation of pseudouridine (psi) in the spliceosomal small nuclear RNAs (snRNA) are reviewed. Multiple psi 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 psi in U5 RNA but not for the modification of U2 RNA. The inhibition of psi formation by the incorporation of 5-fluorouridine in the snRNA is also reviewed.