Palmer MCB-9318858 Abstract An attempt to provide a more rationale resolution to the ongoing controversy of whether introns appeared early or late as a part of the structure of genes will be made. We will develop a comprehensive, computerized intron database. We will test five key predictions of both theories by determining in diverse eukaryotes the intron structure of the gene triphophate isomerase (TPI), the gene which has most often been utilized in this controversy. We will also use the database to evaluate the temporal dynamics of intron gain and loss among the major groups of erkaryotes and, finally, we will examine recent cases of the apparent insertion or sliding of introns in order to gain insight into possible mechanisms. %%% Introns - noncoding sequences that interrupt genes and which are removed at the RNA level via RNA splicing - are the hallmarks of many eukaryotic protein genes. Nowhere is this more true than in humans and other vertebrates, where they occupy 80-90% of a gene's length and number nearly a million. Ever since their discovery 16 years ago (for which a Nobel Prize was awarded this year), a fundamental controversy has raged concerning the evolutionary origin and importance of introns. In order to directly address, and attempt to resolve, this long-standing controversy, we will develop a comprehensive, computerized intron database and use it to assess whether the distribution of introns across eukaryotes best fits the tenets of the competing "introns-early" or "introns-late" theories. In addition, we will test five key predictions of these two theories by determining, in various diverse eukaryotes, the intron structure of the gene TPI that has figured most prominently in this controversy. We will also move beyond this debate by using the intron database to evaluate the temporal dynamics of intron gain and loss among the major groups of eukaryotic, especially animals, plants and fungi. Preliminary analyses suggest a highly episodi c pattern, which raises striking mechanistic and selective questions. Finally, we will examine especially recent cases of the apparent insertion or sliding of introns in order to understand how these events occur. ***
