RNA EDITING - A MECHANISM FOR GRNA-SPECIFIED URIDYLATE INSERTION INTOPRECURSOR MESSENGER-RNA

In the mitochondria of trypanosomatid protozoa the precursors of messe nger RNAs (pre-mRNAs) have their coding information remodeled by the s ite-specific insertion and deletion of uridylate (U) residues. Small t rans-acting guide RNAs (gRNAs) supply the genetic information for this RNA editing. An in vitro system was developed to study the mechanism of U insertion into pre-mRNA. U-insertion editing occurs through a ser ies of enzymatic steps that begin with gRNA-directed pre-mRNA cleavage . Inserted U's are derived from free uridine triphosphate and are adde d to the 3' terminus of a 5' pre-mRNA cleavage product. gRNA specifies edited RNA sequence at the subsequent ligation step by base pairing-m ediated juxtaposition of the 3' cleavage product and the processed 5' cleavage product. gRNA/pre-mRNA chimeras, purported intermediates, see m to be abortive end products of the same reaction.