Elastic moduli renormalization in self-interacting stretchable polyelectrolytes

We study the effect of intersegment interactions on the effective bending a nd stretching moduli of a semiflexible polymer chain with a finite stretchi ng modulus. For an interaction potential of a screened Debye-Huckel type, r enormalization of the stretching modulus is derived on the same level of ap proximation as the celebrated Odijk-Skolnick-Fixman result for the bending modulus. The presence of mesoscopic intersegment interaction potentials cou ples the bending and stretching moduli in a manner different from that pred icted by the macroscopic elasticity theory. We thus advocate a fundamental change in the perspective regarding the dependence of elastic moduli of a f lexible polyelectrolyte on the ionic conditions: stretchability. The theory presented here and its consequences compare favorably with recent experime nts on DNA bending and stretching at not too low salt conditions. [S0021-96 06(00)50244-X].