Wg. Reeve et al., The transcriptional regulator gene phrR in Sinorhizobium meliloti WSM419 is regulated by low pH and other stresses, MICROBIO-UK, 144, 1998, pp. 3335-3342
The phrR gene in Sinorhizobium meliloti (previously known as Rhizobium meli
loti) WSM419, directly downstream from actA, is induced by low ph or certai
n stresses (e.g. high concentrations of Zn2+, Cu2+, H2O2 or ethanol), but n
ot in stationary phase or by other stresses (e.g. phosphate limitation, ele
vated temperature, high concentrations of sucrose or iron). A DNA fragment
containing the wild-type phrR gene could not be cloned and inverse PCR was
therefore used to amplify a 3.5 kb BamHI fragment containing phrR from the
mutant S. meliloti TC2-6 (actA::Tn5). DMA fragments from a BamHI/SalI diges
t of the amplified product were cloned into pUK21 and sequenced. The phrR o
pen reading frame contiguous to actA appears to code for a 15.2 kDa protein
showing significant identity with the proteins encoded by y4wC and y4aM in
Rhizobium sp. NGR234. All three proteins resemble transcriptional regulato
rs in containing a DNA-binding helix-turn-helix motif similar to that repor
ted for URF4 in Rhodospirillum rubrum and repressors in coliphage.