PRE-TRNA SPLICING : VARIATION ON A THEME OR EXCEPTION TO THE RULE ?

: There has been a growing recognition that there are many conserved features among apparently diverse RNA splicing systems, suggesting that they may have a common origin. However, pre-tRNA splicing is an apparent exception in nearly all respects. Features of this unique class should be considered in any comprehensive discussion of the origin(s) of splicing and its implications for the evolution of gene structure.