  A theory of condensation and resolubilization of a dilute DNA solution with
growing concentration of multivalent cations, N is suggested. It is based on a
new theory of screening of a macroion by multivalent cations, which shows that
due to strong cation correlations at the surface of DNA the net charge of DNA
changes sign at some small concentration of cations N_0. DNA condensation takes
place in the vicinity of N_0, where absolute value of the DNA net charge is
small and the correlation induced short range attraction dominates the Coulomb
repulsion. At N > N_0 positive DNA should move in the oppisite direction in an
electrophoresis experiment. From comparison of our theory with experimental
values of condensation and resolubilization thresholds for DNA solution
containing Spe$^{4+}$, we obtain that N_0 = 3.2 mM and that the energy of DNA
condensation per nucleotide is $0.07 k_B T$.
