48073
Presenter: Thuy Tran T. Hoang
Mentor: Alan Barbour
Title: Transgenic Expression of RecA of Borrelia burgdorferi and Borrelia hermsii in Escherichia coli
The recA gene is the major gene in bacteria that promotes homologous recombination. The RecA
protein is highly conserved among all bacteria, including pathogenic spirochetes Borrelia burgdorferi and
Borrelia hermsii, the agents of Lyme Borreliosis and relapsing fever, respectively. E. coli expressing the
RecA gene from B. hermsii and B. burgdorferi were subjected to DNA damage and recombination
assays. Results of these studies show that the survival of E. coli expressing B. hermsii RecA was
significantly less than E. coli expressing B. burgdorferi RecA, while recombination levels were the same
for both proteins. Examination of the deduced protein sequence of B. hermsii RecA revealed a
glutamine for lysine substitution at position 152. This residue is located between the ATP hydrolysis
and a DNA binding site. We hypothesized that difference in complementation between the two
Borrelia species is due to the K152Q substitution found in the RecA of B. hermsii. For E. coli
expressing modified B. burgdorferi RecA, DNA damage repair assays show that complementation is
adversely affected by the mutant protein. Increased resistance to the chemical agent methyl methan
sulfonate is observed in E. coli expressing modified B. hermsii RecA. However, in both UV survival
assays and in homologous recombination assays, no statistical difference was observed between
modified and wild-type proteins activity. From these complementation studies in the heterologous E.
coli system, it appears that RecA functions differently when catalyzing homologous recombination
and homologous recombination DNA repair.