Committee:

iii Jill Zeilstra-Ryalls, Ph.D, Advisor The common precursor to all tetrapyrroles, essential biomolecules that include hemes, chlorophylls, and corrinoids, is 5-aminolevulinic acid (ALA). In the facultative phototroph Rhodobacter sphaeroides, ALA formation is catalyzed by ALA synthase. Not all strains of R. sphaeroides have the same genomic content of ALA synthase genes; wild type strains 2.4.1 and 2.4.9 have two, hemA and hemT, while strain 2.4.3 has only one, hemA. The upstream regions of hemA and also hemT (when present) differ among these strains, which suggest their expression may not be the same in every strain. Therefore, to understand how the cell produces the proper amounts of ALA to support growth, while maintaining adequate metabolic flexibility, investigations into the significance of these differences were carried out using lacZ transcription reporter plasmids involving the upstream sequences of the ALA synthase genes from all three strains. The assays of β-galactosidase activities in strains harboring the reporter plasmid