Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Biological Sciences

First Advisor

Alan J. Biel


In Rhodobacter capsulatus, a purple nonsulfur bacterium, the tetrapyrrole pathway yields four end products: siroheme, vitamin B12, heme and bacteriochlorophyll. Growth of R. capsulatus under low oxygen tension increases carbon flow through the tetrapyrrole pathway up to 100 fold. The mechanism(s) for this regulation is currently unknown. One regulatory mechanism could be transcriptional control of one or more of the genes in the common portion of the tetrapyrrole pathway. The fifth gene in the pathway, hemE, has been cloned by complementation of an Escherichia coli hemE::miniTn10 mutant. Sequence data of hemE revealed the presence of an upstream palindrome that is homologous to consensus sequences reported upstream of seven other R. capsulatus bch, crt and puc genes. Under low oxygen tension, transcription of the palindrome-containing bch and crt genes is increased 2 to 4 fold and transcription of the puc gene is increased 40 fold. It has been speculated that the upstream motif represents a binding site for a regulatory protein involved in oxygen-mediated transcriptional control. Both dot blot analysis and chloramphenicol acetyltransferase assays were used to measure transcription of the R. capsulatus hemE gene under conditions of high and low oxygen tensions. The results indicated that transcription is not regulated by oxygen. If the palindrome upstream of the R. capsulatus hemE gene is a binding site for a regulatory protein, it is not a protein which responds to changes in oxygen tension.