Recognition of tRNA Precursors: A Role for the Intron

Abstract

Most eukaryotic genes contain introns that interrupt the continuity of the genetic information. Introns are removed from a precursor RNA transcript by a process called splicing, whereby the intron is clipped out and the exons are rejoined to give the functional RNA molecule. There are three distinct mechanisms of RNA splicing (1-3). In the self-splicing mechanism, discovered by Cech, the splicing process relies on the intron to take on a complex structure and to catalyze its own removal. In mRNA splicing in the eukaryotic nucleus, the pre-mRNA molecule is assembled into a large complex structure, the spliceosome, and components of the spliceosome, probably one or more of the small nuclear RNA's, catalyze the splicing reaction. In contrast, the small introns that interrupt the anticodon loops of eukaryotic precursor tRNA's are removed by a comparatively simple and familiar enzymatic process in which an endonuclease cleaves the two splice junctions and an ATP-dependent ligase joins the two exons.