title: DNA condensation by polyamines: a laser light scattering study of structural effects.
abstract: Polyamines such as spermidine and spermine are abundant in living cells and are believed to aid in the dense packaging of cellular DNA. DNA condensation is a prerequisite for the transport of gene vectors in living cells. To elucidate the structural features of polyamines governing DNA condensation, we studied the collapse of lambda-DNA by spermine and a series of its homologues, H2N(CH2)3NH(CH2)n=2-12NH(CH2)3NH2 (n = 4 for spermine), using static and dynamic light scattering techniques. All polyamines provoked DNA condensation; however, their efficacy varied with the structural geometry of the polyamine. In 10 mM sodium cacodylate buffer, the EC50 values for DNA condensation were comparable (4 +/- 1 microM) for spermine homologues with n = 4-8, whereas the lower and higher homologues provoked DNA condensation at higher EC50 values. The EC50 values increased with an increase in the monovalent ion (Na+) concentration in the buffer. The slope of a plot of log [EC50(polyamine4+)] against log [Na+] was approximately 1.5 for polyamines with even number values of n, whereas the slope value was approximately 1 for compounds with odd number values of n. Dynamic light scattering measurements showed the presence of compact particles with hydrodynamic radii (Rh) of about 40-50 nm for compounds with n = 3-6. Rh increased with further increase in methylene chain length separating the secondary amino groups of the polyamines (Rh = 60-70 nm for n = 7-10 and >100 nm for n = 11 and 12). Determination of the relative binding affinity of polyamines to DNA using an ethidium bromide displacement assay showed that homologues with n = 2 and 3 as well as those with n > 7 had significantly lower DNA binding affinity compared to spermine and homologues with n = 5 and 6. These data suggest that the chemical structure of isovalent polyamines exerts a profound influence on their ability to recognize and condense DNA, and on the size of the DNA condensates formed in aqueous solution.
authors.affiliation: Department of Medicine, The Cancer Institute of New Jersey, University of Medicine and Dentistry of New Jersey-Robert Wood Johnson Medical School, New Brunswick, New Jersey 08903, USA.
authors.forename: V
authors.initials: V
authors.lastname: Vijayanathan
authors.forename: T
authors.initials: T
authors.lastname: Thomas
authors.forename: A
authors.initials: A
authors.lastname: Shirahata
authors.forename: T J
authors.initials: TJ
authors.lastname: Thomas
mesh_terms: D010582:Bacteriophage lambda / Q000187:drug effects / Q000235:genetics; D001665:Binding Sites; D004279:DNA, Viral / Q000737:chemistry / Q000187:drug effects*; D008027:Light; D009994:Osmolar Concentration; D011073:Polyamines / Q000494:pharmacology*; D012542:Scattering, Radiation; D013096:Spermine / Q000494:pharmacology
chemical_list: D004279:DNA, Viral; D011073:Polyamines; D013096:Spermine