Antirestriction Activity of Metalloregulatory
Proteins ArsR and MerR

S. M. Rastorguev¹, T. A. Letuchaya¹, G. Ya. Kholodii², S. Z. Mindlin²,
V. G. Nikiforov², and G. B. Zavil’gel’skii¹

¹ State Research Center GosNIIGenetika, Moscow, 113545 Russia
² Institute of Molecular Genetics, Russian Academy of Sciences, Moscow, 123182 Russia

Received September 29, 1998

Abstract—The antirestriction activity of ArsR (a repressor of the ars operon conferring resistance to arsenite
and arsenate) encoded by arsR of conjugative plasmid R773 (IncFI) was estimated. When cloned in a multicopy
vector under the control of the lac promoter, arsR alleviated EcoK restriction of nonmodified phage DNA 15–
20 times; i.e., its effect was comparable to that of the EcoRI–PstI fragment of conjugative plasmid R64 cloned
in the same vector. Cloned merR for a transcriptional regulator of the ars operon (mercury resistance of bacte-
ria) also alleviated type I restriction, but to a lesser extent. The arsR, merR, and ard genes (ardA and ardB for
antirestriction proteins) are nonhomologous. However, an “antirestriction motif” of nine amino acid residues,
characteristic of the Ard proteins, was also found in ArsR and MerR. Since this motif (24-L-L-R-E-M-G-E-L-
C) overlaps with the binding center for arsenic compounds (30-E-L-C-V-C-D-L-C) in ArsR, the protein did not
repress the ars operon and did not alleviate restriction in the presence of meta-arsenite.

Key words: ars operon, mer operon, arsR, merR, metalloregulatory proteins, antirestriction, ard, antirestriction
motif

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