In order to elucidate the role of in vivo interaction of single-strand DNA binding protein with DNA polymerase II isogenic strains of Escherichia coli were constructed combining the ssb+, ssb-1 alleles with DNA polymerases I or II mutations; their radiosensitivity and a level of UV-induced DNA degradation were studied. Received findings suggest a functional antagonism of SSB-proteins depending on intracellular conditions (from the balance of DNA and protein synthesis). The SSB-proteins provide the stability of the genome or, vice versa, perturb the stability of the genome, by degrading of DNA macromolecules.