A MarR-like transcriptional regulator involved in the detoxification of aromatic compounds in Sulfolobus solfataricus

Dipartimento di Biologia Strutturale e Funzionale, Università degli Studi di Napoli Federico II, Complesso Universitario Monte S. Angelo, Via Cinthia, 80126 Napoli, Italy, Istituto di Biochimica delle Proteine, CNR, Via Pietro Castellino 111, 80131, Napoli, Italy

^* To whom correspondence should be addressed. Email: fiogabri{at}unina.it.

	Abstract

A DNA binding protein, BldR, was identified in the crenarchaeon Sulfolobus solfataricus as a protein 5 to 10 fold more abundant in cells grown in the presence of toxic aldehydes; it binds to regulatory sequences located upstream of an alcohol dehydrogenase gene (Sso2536). BldR is homologous to bacterial representatives of the MarR (Multiple Antibiotic Resistance) family of transcriptional regulators, that mediate response to multiple environmental stresses. Transcriptional analysis revealed that the bldR gene was transcribed in a bi-cistronic unit composed of the genes encoding the transcriptional regulator (Sso1352) and a putative multidrug transporter (Sso1351) upstream. By homology to bacterial counterparts the bi-cistron was named Mar-like operon. The Mar-like operon expression was found to be increased at least 10 fold in response to chemical stress by aromatic aldehydes. In the same growth conditions, similar enhanced in vivo levels of Sso2536 transcript were also measured.

The gene encoding BldR was expressed in E. coli and the recombinant protein purified to homogeneity. DNA binding assays demonstrated that the protein is indeed a transcription factor able to recognize site-specifically both the Sso2536 and Mar-like promoters at sites containing consensus palindromic sequences. The benzaldehyde, substrate of Sso2536, stimulates DNA binding of BldR at both promoters. The role of BldR in the auto- as well as in the regulation of Sso2536, together with results of increased operon and gene expression under conditions of exposure to aromatic aldehydes, indicate a novel coordinate regulatory mechanism in cell defense against stress by aromatic compounds.