5-Aminolevulinic acid (ALA) is the first committed intermediate in the biosynthesis of the hemes, chlorophylls, corrins and other naturally-occurring cyclic and linear tetrapyrrolic compounds. In animals, yeast and some bacteria, ALA is synthesized from glycine and succinyl CoA (C4 pathway). In higher plants, algae and cyanobacteria it is synthesized from glutamate (C5 pathway). It had been assumed that E. coli followed the C4 pathway, but it has been shown conclusively, using radiolabelling experiments, that E. coli uses the C5 pathway, although it can use a foreign C4 pathway gene when it is introduced on a plasmid. This project will (1) isolate and characterize mutants in ALA biosynthesis, (2) use them to clone the C5 pathway genes, (3) identify and characterize the gene products, (4) reconstitute and characterize the C5 enzymatic pathway, and (5) use in vivo and in vitro techniques to study levels of control (transcriptional, translational and enzymatic) of ALA biosynthesis in E. coli. Heme is a necessary component of a number of important biological compounds. Chlorophyll and hemoglobin are two examples of heme proteins. This research will examine the early steps of heme biosynthesis in order to better understand the components of the pathway and its regulation. These studies are important agriculturally because of the potential for improved crop yields through greater protosynthetic efficiency. It will also be of value in the medical field where an understanding of heme biosynthesis is necessary to the understanding of genetic disorders which are associated with the pathway.