FIG 5.

ArsR binds a sequence downstream of the poly(T) tract associated with the sabA promoter. (A) Nested biotin-labeled probes of the sabA promoter region were used in EMSA to localize the ArsR binding site. A 156-bp sabA probe (−20 to +135) was electrophoresed alone (lane 1), with rArsR (lane 2), with rArsR and a 500-fold excess of unlabeled probe as a specific competitor (lane 3), and with rArsR and a 500-fold excess of Epstein-Barr virus nuclear antigen DNA as a nonspecific DNA competitor (lane 4). rArsR-DNA binding reactions in lanes 5 to 8 were run identically except for the use of a 5′-truncated (to +39 to +135) sabA probe to demonstrate the loss of rArsR binding with the loss of the upstream 60 bp. (B) Proposed binding site of ArsR in the 5′ untranslated region of sabA. Converging arrows indicate a region of partial dyad symmetry within the region bound by rArsR. The underlined sequence is the 5′ end of the truncated probe used in lanes 5 to 8 in panel A.