Book of Abstracts: Albany 2007
June 19-23 2007
Bacterial protein HU dictates the morphology of DNA condensates produced by crowding agents and polyamines
Controlling the size and shape of DNA condensates is important in vivo and for the improvement of nonviral gene delivery. Here, we demonstrate that the morphology of DNA condensates, formed under a variety of conditions, is shifted completely from toroids to rods if the bacterial protein HU is present during condensation. HU is a nonsequence-specific DNA binding protein that exhibits high affinity for discontinuous DNA substrates and can sharply bend DNA upon binding. Alone, HU does not condense DNA into densely packed particles; however, less than one HU dimer per 225 bp of DNA is sufficient to completely control condensate morphology when DNA is condensed by spermidine. We propose that rods are favored in the presence of HU because rods contain sharply bent DNA, whereas toroids contain only smoothly bent DNA. We are now investigating whether the IHF protein, a member of the same protein family as HU with identical secondary structure, has a similar affect on condensate morphology in the presence of polyamines. The results presented illustrate the utility of naturally derived proteins for controlling the shape of DNA condensates formed in vitro. HU is a highly conserved protein in bacteria that is implicated along with IHF in the compaction and shaping of nucleoid structure. However, the exact role of HU and IHF in chromosome compaction is not well understood. Our demonstration that HU governs DNA condensation in vitro also suggests a mechanism by which HU could act as an architectural protein for bacterial chromosome compaction and organization in vivo.
1School of Chemistry and Biochemistry, Parker H. Petit Institute of Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, Georgia 30332-0400