9723034 Huvos The evolution of two genomic regions which are known to contain segments of DNA that undergo developmental DNA deletions in T. thermophila will be examined. One region contains a single developmentally eliminated segment, the other region contains two such segments. The three segments have different characteristic features, i.e. are likely to belong to different classes of rearrangements. A comparison will be made of these two regions between T. thermophila and two or more of its close relatives. Preliminary analysis of the two regions has been undertaken using the Southern hybridization technique. Results from this analysis indicate that in these regions a variety of evolutionary scenarios are possible in the species intended for study. Comparative analysis of homologous regions where there is a rearrangement in T. thermophila, but not in its relative (or vice versa) is the major target of this work. Examination of such regions will lead to the understanding of the molecular events that generate or disrupt developmental rearrangement sites during evolution, and will indicate whether these evets are associated with insertion of developmentally eliminated sequence elements. These results will be compared to recent studies on the evolution of DA deletions in a distantly related group of ciliated protozoans which contain different types of developmentally eliminated sequences. Rearrangements homologous to those found in T. thermophila will be used to identify conserved features of the developmentally eliminated sequences that may be involved in the process of rearrangement and to examine the sequence heterogeneity generated at the deletion junctions. The results will be experimentally tested by manipulating the sequences. Programmed DNA rearrangements occur as part of normal development in a variety of organisms, including the mammalian immune system. Unprogrammed rearrangements are an important force in the evolution of genomes and are associated with pathological states, suc h as oncogenesis. Development in ciliated protozoans involves extensive programmed genome reorganization which makes these organisms good models for investigating such rearrangements. The study of evolutionary changes of programmed elimination events in these organisms provides an opportunity to explore the relationship between programmed and unprogrammed rearrangements.
