Brucei-group trypanosomes are medically important parasites and useful for the study of the mitochondrial genetic system. They are especially useful for the study of mitochondrial mutation and regulation of mitochondrial gene expression. Dyskinetoplastic mutant (dk) Trypanosoma brucei has grossly altered mitochondial DNA and lacks the ability to develop a normal mitochondrial respiratory system. It can, however, grow in the mammalian host. I propose to determine the genetic content of normal and dk mitochondrial DNA and analyze the sequence and physical structure of this DNA as it is organized into the mitochondrial genome. The normal and mutant DNA will be analyzed by a variety of techniques including renaturation kinetics and restriction endonuclease analysis. The specific alterations suffered by the dk mitochondrial DNA will be analyzed by molecular hybridization employing normal and mutant DNA as well as specific molecular probes. Physical alterations will also be analyzed by electron microscopy. The information derived from these studies should contribute to our understanding of the structure and function of the mitochondrial genetic system and the mechanisms by which it can be altered.