Evolution of Aromatic Biosynthesis and Regulation in Prokaryotes

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Dr. Jensen proposes to utilize the cataloging of oligonucleotide sequence. The strong conservation of ribosomal RNA through evolutionary time is the basis for assembly of a credible phylogenetic tree for prokaryotes. Slow changes in rRNA can be quantitated in the form of SAB values by oligonucleotide cataloging, thus providing an evolutionary scale against which the evolution of other gene-product systems can be measured. It is possible now for the first time to reconstruct in prokaryotes the events in the evolution of biochemical-pathway arrangement and biochemical-pathway regulation. We propose to obtain data that will permit such evolutionary deductions to be made with respect to the pathway for biosynthesis of aromatic amino acids. This will be carried out in a large but manageable division of prokaryotes, the "purple" bacteria. Data already obtained allow construction of a working model for deductions about the evolution of (i) tyrosine-pathway cofactor specificity, (ii) DAHP synthase isozymes, (iii) the phenylalanine pathway and its regulation, and (iv) the tyrosine pathway and its regulation. As new cataloging data identify brance positions on the tree where gaps limit interpretations, we will proceed with analysis of these organisms. At shallow levels of divergence, rRNA/DNA hybridization will probably be more appropriate for identification of evolutionary points of divergence in correlation with fine-tuned instances of recent biochemical change.