Before revision:  Additionally, strong repulsions between DNA and divalent co-ions and among divalent co-ions themselves leads to a {\em depletion} of negative ions near DNA surface as compared to the case without divalent co-ions.
After revision:  The overcharging of DNA by multivalent counterions is also reduced in the presence of divalent co-ions. Strong repulsions between DNA and divalent co-ions and among divalent co-ions themselves leads to a {\em depletion} of negative ions near DNA surface as compared to the case without divalent co-ions.