Antirestriction activity of metalloregulatory proteins ArsR and MerR

The antirestriction activity of ArsR (a repressor of the ars operon conferr ing resistance to arsenite and arsenate) encoded by arsR of conjugative pla smid R773 (IncFI) was estimated. When cloned in a multicopy vector under th e control of the lac promoter, arsR alleviated EcoK restriction of nonmodif ied phage lambda DNA 15-20 times; i.e., its effect was comparable to that o f the EcoRI-PstI fragment of conjugative plasmid R64 cloned in the same vec tor. Cloned merR for a transcriptional regulator of the ars operon (mercury resistance of bacteria) also alleviated type I restriction, but to a lesse r extent. The arsR, meR, and ard genes (ardA and ardB for antirestriction p roteins) are nonhomologous. However, an "antirestriction motif" of nine ami no acid residues, characteristic of the Ard proteins, was also found in Ars R and MerR. Since this motif (24-L-L-R-E-M-G-E-L-C) overlaps with the bindi ng center for arsenic compounds (30-E-L-C-V-C-D-L-C) in ArsR, the protein d id not repress the ars operon and did not alleviate restriction in the pres ence of meta-arsenite.