Polyamine ions such as spermidine³⁺, along with monovalent and divalent salt ions, screen the negatively charged backbone of dsDNA and thereby facilitate processes in which DNA is confined in small spaces, such as viral DNA packaging. We use optical tweezers to directly manipulate single DNA molecules and have made preliminary measurements of the effect of spermidine on DNA elasticity, condensation, and viral packaging. We determine the concentration of spermidine³⁺ at which dsDNA condenses in the presence of Mg²⁺ and Na⁺ and report a monotonic increase in stretch modulus and decrease in persistence length at incremental spermidine concentrations up to the concentration at which dsDNA condenses. We also discuss the effect of spermidine on DNA packaging in bacteriophage phi29.

Date Published: 10 October 2012
PDF: 9 pages
Proc. SPIE 8458, Optical Trapping and Optical Micromanipulation IX, 845818 (10 October 2012); doi: 10.1117/12.930381

Published in SPIE Proceedings Vol. 8458:
Optical Trapping and Optical Micromanipulation IX
Kishan Dholakia; Gabriel C. Spalding, Editor(s)