D-block metal cations are essential for most biological processes; however, excessive metal exposure can be deleterious to the survival of microorganisms. To tightly control heavy metal regulation, prokaryotic organisms have developed several mechanisms to sense and adapt to changes in intracellular and extracellular metal concentrations. The ferric uptake regulator superfamily of transcription factors associates with DNA when complexed with a regulatory metal cofactor and often represses the transcription of genes involved in metal transport, thus providing a genomic response to an environmental stressor. Although extensively studied in mesothermic organisms, there is little information describing ferric uptake regulator homologs in thermophiles. In this study, we biochemically characterize the ferric uptake regulator homolog TTHA1292 in the extreme thermophile Thermus thermophilus HB8. We identify the preferred DNA-binding sequence of TTHA1292 using the combinatorial approach, restriction endonuclease, protection, selection, and amplification (REPSA). We map this sequence to the Thermus thermophilus HB8 genome and identify the TTHA1292 transcription regulatory network, which includes the zinc ABC transporter subunit genes TTHA0596 and TTHA0453/4. We formally implicate TTHA1292 as a zinc uptake regulator and show that zinc coordination is critical for the multimerization of TTHA1292 dimers on DNA in vitro and transcription repression in vivo. IMPORTANCE Discovering how organisms sense and adapt to their environments is paramount to understanding biology. Thermophilic organisms have adapted to survive at elevated temperatures (>50°C); however, our understanding of how these organisms adapt to changes in their environment is limited. In this study, we identify a zinc uptake regulator in the extreme thermophile Thermus thermophilus HB8 that provides a genomic response to fluctuations in zinc availability. These results provide insights into thermophile biology, as well as the zinc uptake regulator family of proteins.
Keywords: Thermus thermophilus; metalloregulation; transcriptional regulation; zinc uptake regulator.