[Proteolytic control of the antirestriction activity of Tn2l, Tn5053, Tn5045 Tn501 TN402 non-conjugative transposons]

Conjugative plasmids and conjugative transposons contain the genes, which products specifically inhibit the type I restriction--modification systems. Here is shown that non-conjugative transposons Tn2l, Tn5053, Tn5045, Tn501, Tn402 partially inhibit the restriction activity of the type I restriction-modification endonuclease EcoKI (R2M2S1) in Escherichia coli cells K12 (the phenomenon of restriction alleviation, RA). Antirestriction activity of the transposons is determined by the MerR and ArdD proteins. Antirestriction activity of transposons is absent in mutants E. coli K12 clpX and clpP and is decreased in mutants E. coli K12 recA, recBC and dnaQ (mutD). 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. RA effect is determined by the ClpXP-dependent degradation of the endonuclease activity R subunit of EcoKI (R2M2S1).