Vfr specifically binds to the PA2782-mep72 upstream region. (A) Nucleotide sequence of the PA2782-mep72 upstream region with the putative Vfr binding site indicated by a yellow box. The Vfr consensus sequence is aligned beneath with matching bases in bold; W, purine (A, G); Y, pyrimidine (T, C); N, any base. The −10 and −35 sequences are indicated by dotted lines. The GTG start codon for PA2782 is indicated in blue. (B) Diagram of the 98-bp region upstream of PA2782-mep72 (Probe I); yellow line, Vfr consensus sequence; dotted orange lines, the −10 and −35 sequences. (C) Recombinant Vfr binds to the PA2782-mep72 upstream region. Probe I was prepared by PCR, purified, and radiolabeled. EMSA binding reactions contained approximately 105-107 c.p.m. of labeled probe plus 10 ng purified rVfr (Methods). Samples were separated by 5% SDS-PAGE with 20 mM cAMP added to the running buffer to promote Vfr binding. Lanes: 1) Probe I alone; 2) Probe I plus rVfr; 3) Probe I and rVfr plus excess of unlabelled probe; 4), Probe I plus rVfr (compiled from a separate experiment in which no cAMP was added to the running buffer). Red arrow, Probe I-rVfr complex; blue arrow, unbound Probe I. (D) Compiled autoradiographs of gel shift assays using Probes I, II, III, and VI. EMSA were run as described in (C) and Methods. Each segment shows probe alone (lane 1) and probe plus 10 ng rVfr (lane 2). Red arrows indicate probe-rVfr complexes; blue arrows, unbound probes. (E) Diagram of the nested deletion analysis used to further localize rVfr binding. The matching bases of the 5-bp imperfect inverted repeat (TGGCG/CGCTG) are in red and underlined. These bases are bracketed by two direct repeats (TG-N3-CA/TG-N3-CA) indicated in blue and underlined.
Balyimez et al. BMC Microbiology 2013 13:269 doi:10.1186/1471-2180-13-269