The proposed research will study three critical problems in the field of molecular genetics: the mechanism of "illegitimate" recombination catalyzed by transposable elements, the mechanism of transcription initiation and the mechanism of translation initiation. Transposable elements are genetic entities that are widespread throughout nature which can catalyze numerous types of genome rearrangements and thus have been implicated in germline mutations (important for evolution) and somatic cell mutations (important in oncogenesis). Our projects will use genetic and biochemical approaches to elucidate the molecular mechanism of illegitimate recombination encoded by one model system--the bacterial transposon Tn5. Transcription initiation is the first step in gene expression. We will be studying how promoter structure (the DNA sequence recognized by RNA polymerase) affects this process. We will also be examining how regulatory protein-DNA interactions and competitive RNA polymerase-DNA interactions modulate this process. Translation initiation is also a crucial step in gene expression in which the rate of protein systhesis from a particular mRNA is modualted. The structure (both 1 degree and 2 degree) of the mRNA is an important determinant of the rate of this process. We will analyze mutations affecting the structure of the lacZ mRNA in an attempt to understand this event.