Conjugative plasmids and conjugative transposons contain the genes, whose products specifically inhibit the type-I restriction-modification systems. Here, it is shown that non-conjugative transposons Tn21, Tn5053, Tn5045, Tn501, and Tn402 partially inhibit the restriction activity of the type-I restriction-modification endonuclease EcoKI (R₂M₂S₁) into Escherichia coli K12 cells (phenomenon of restriction alleviation, RA). The antirestriction activity of the transposons is determined by the MerR and ArdD proteins. The antirestiction activity of transposons is absent in the clpX and clpP E. coli K12 mutants and is decreased in recA, recBC, and dnaQ (mutD) E. coli K12 mutants. The induction of the RA in response to the MerR and ArdD activities is consistent with the production of unmodified target sequences following DNA repair and DNA synthesis associated with recombination repair or replication errors. The RA effect is determined by the ClpXP-dependent degradation of the endonuclease activity R subunit of EcoKI (R₂M₂S₁).