| Group II introns are self-splicing ribozymes that can function as mobile retroelements. They are typically found in archaebacteria, eubacteria, and lower eukaryotic organelles. In this dissertation, three different aspects of group II introns were studied. The first involved the analysis of the evolution of group II intron RNA structures. In this project, I determined that group II intron RNA structures coevolved with their intron-encoded reverse transcriptases. This led to the formulation of the retroelement ancestor hypothesis which postulates that ORF-containing group II introns originated in bacteria and gave rise to ORF-containing and ORF-less group II introns in the organelles of higher eukaryotes. In the second part of this dissertation, I discuss my discovery of a novel family of group II introns encoding group I intron-type LAGLIDADG endonuclease ORFs instead of the typical RT ORFs. The final project involved the biochemical characterization of a putatively primitive group IIC intron ribozyme from the organism Bacillus halodurans. This intron belongs to a class whose members are always found inserted after intrinsic transcription terminators. Here, I present evidence that the ribozyme itself is able to recognize the terminator structure for 5' splice site selection. Additionally, the terminator seems to be required for the transition to the second step of splicing. |
