Gene Duplication, Divergence, and What Lies in Between

• Main Author: Morgenthaler, Andrew Bank
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2020
• Subjects: Biochemistry; Evolution & development; Evolution and Development; Molecular biology
• ISBN: 9798645452117

Life has repeatedly evolved new functions throughout its history, allowing life to survive and diversify for 3.8 billion years. The evolution of a novel function frequently requires the evolution of a new gene that encodes for an enzyme with a new function. New enzymes often evolve by amplification and divergence of preexisting genes encoding enzymes with a weak ability to provide a new function. Previous experimental studies have followed the evolutionary trajectory of an amplified gene, but have not considered mutations elsewhere in the genome when fitness is limited by an evolving gene. I have evolved a strain of Escherichia coli in which a secondary promiscuous activity has been recruited to serve an essential function. The gene encoding the ‘weak-link’ enzyme amplified in all eight populations, but mutations improving the newly needed activity occurred in only one. Most adaptive mutations occurred elsewhere in the genome to improve flux through the bottlenecked pathway. Finally, I compared the evolution of a strain of Escherichia coli grown in two different selective conditions: one in which the original function of an evolving enzyme is no longer required for growth and one in which both the new and original functions are required for growth. While the amplified region of the genome surrounding the evolving gene differed between the two selective conditions, most of the adaptive mutations in the two conditions were similar, suggesting the new activity of the evolving enzyme is more rate-limiting for growth than its native activity. Together these results depict how an organism evolves during the evolution of a new enzymatic function.