Protamine-induced condensation and decondensation of the same DNA molecule

The DNA sperm and certain viruses is condensed by arginine-rich proteins in to toroidal subunits, a form of packaging that inactivates their entire gen ome. Individual DNA molecules were manipulated with an optical trap to exam ine the kinetics of torus formation induced by the binding of protamine and a subset of its DNA binding domain, Arg(6). Condensation and decondensatio n experiments with lambda-phage DNA show that toroid formation and stabilit y are influenced by the number of arginine-rich anchoring domains in protam ine. The results explain why protamines contain so much arginine and sugges t that these proteins must be actively removed from sperm chromatin after f ertilization.