Little variation was observed during the replicate experiments. The standard deviation for

the antirestriction results is 25% or less. Data on antirestriction activity of the recombinant plasmid pKLH53.1, containing Tn5053, are given in Table 2. The factor of restriction relief (R) is about 100. We suspected that the nucleotide sequence of the mercury-resistance transposon Tn5053 contains a fragment encoding an antirestriction protein. We used both insertion and deletion mutants of Tn5053 for all transposition genes (tni) as well as plasmid constructs containing various fragments of the Tn5053 DNA, while searching for the locus responsible for the antirestriction activity (Fig. 1). The results of searches selleck chemical for the determinant of antirestriction activity Ku-0059436 purchase within Tn5053 are shown in Table 2. It is evident that neither insertion (plasmids pKLH53.1tniA, pKLH53.1tniB2) or deletion (plasmids pKLH53.1tniQ2 and pKLH53.1tniQ1) mutations of the tni genes have any effect on antirestriction activity: about 100-fold decrease in EcoKI restriction level is preserved. Deletion of the major part of the mer operon (plasmid

pTLΔHindIII) completely removed the effect of antirestriction (Table 2). We assumed that the location of the gene coding for an antirestriction protein is within the mer operon. However, the recombinant plasmids pTLHindIII-ClaI and pTL2.5 with fragments HindIII-ClaI and HindIII from the mer operon (without the merR gene) in vector pUC19 show no antirestriction effect (Table 2). No antirestriction effect was also observed for the hybrid plasmid pKLH53.2, containing all the genes tni Tn5053 under its own promoter (in vector pACYC184; Fig. 1, Table 2). A paradox appeared: the mer operon together with the transposition genes (tni) of Tn5053 produce an antirestriction effect, while the plasmids with separately cloned mer operon or tni genes show no antirestriction effect.

We considered that the nucleotide sequence coding for the ORF with antirestriction activity is located within the region of the tni genes, but orientated in reverse to the direction of transcription of the tni genes. Consequently, the coding strand for this ORF is the same as for the mer operon. If so, transcription of this DNA fragment passes Dipeptidyl peptidase from the side of the mer operon. We analysed the DNA sequence from the region of the tni genes of Tn5053 in reverse direction, and found several orfs. Of main interest was orf-5, encoding a negatively charged protein with a motif close to the antirestriction motif of the proteins Ard (Fig. 2). The protein ORF-5 contains 147 amino acid residues of summary charge −1. It is encoded by orf-5 at positions 7511–7954 on the complementary strand of the tniA gene (positions numbered according to the nucleotide sequence of Tn5053, deposited in DBJ/EMBL/GenBank under accession number L40585).