Quantitative analyses of the interaction of the Escherichia coli monomeric PriA helicase with the double-stranded DNA (dsDNA) have been studied with fluorescent dsDNA oligomers, using quantitative fluorescence titrations, analytical ultracentrifugation, and fluorescence resonance energy transfer methods. The experiments have been performed with different dsDNA oligomers, long enough, to encompass the total DNA-binding site, as well as the DNA-binding site proper of the enzyme. Interactions with the dsDNA oligomers were examined as a function of different temperature, salts, and nucleotide cofactors. The stoichimetry of the PriA helicase - dsDNA is different from the stoichiometry of the analogous complexes with the ss conformation of the nucleic acid, indicating a very different orientation of the helicase on the dsDNA. Surprisingly, the intrinsic dsDNA-affinity of the enzyme is dramatically higher than the ssDNA affinity, indicating strong selectivity of the helicase for the dsDNA conformation of the nucleic acid. The intrinsic affinities are salt-dependent and the formation of the PriA helicase - dsDNA complex is accompanied by a net ion change. Moreover, the presence of nucleotide cofactors has a profound effect on the dsDNA interactions of the enzyme with the DNA. The interactions of the PriA helicase with the dsDNA are characterized by very weak, if any, cooperative interactions. The significance of these results on activities of the PriA helicase in the cell metabolism is discussed.