Briana Burton

How do cells move one of the largest and most hydrophilic biological molecules across hydrophobic membrane barriers? This is the broad question our laboratory seeks to understand. In bacteria alone, this process is involved in the transfer of antibiotic resistance, spore formation, and proper chromosome segregation during growth. Yet, very little is known about the molecular mechanism of DNA translocation across membranes in any system, as tools to study the mechanism of DNA transporters in their biological context at the membrane have been lacking. We combine in vitro and in vivo biochemistry, microscopy, microbiology and molecular biology to study these DNA transport complexes.

DNA transport during sporulation

Proper chromosome segregation is essential for successful cell division in all organisms. Interestingly, bacterial cells often form a division septum prior to completion of DNA segregation. Sporulating Bacillus subtilis cells provide an extreme example of this phenomenon in that they must transport more than 3 Megabases of a chromosome across a division septum and into the small cellular compartment that will become the spore. SpoIIIE, a member of a large family of bacterial and archeal membrane-bound ATPases (FtsK/SpoIIIE), is required for active transport of the chromosomal DNA at the division septum during sporulation. Using quantitative fluorescence microscopy, and in vivo DNA transport assays to study the oligomeric state and transport properties of the SpoIIIE complex led to the very surprising and novel result that the DNA is transported across two membranes during sporulation. These data predict a new model for DNA transport in which the transmembrane segments of the transporter form linked DNA-conducting channels across the two lipid bilayers of the septum. This system provides a unique opportunity to tackle this interesting phenomenon using complimentary in vivo and in vitro approaches and to address issues which have significant implications for our understanding of how cells efficiently move of large nucleic acids across membranes.