RT Journal Article SR Electronic T1 Molecular control of gene expression by Brucella BaaR, an IclR-family repressor JF bioRxiv FD Cold Spring Harbor Laboratory SP 251942 DO 10.1101/251942 A1 Julien Herrou A1 Daniel M. Czyż A1 Aretha Fiebig A1 Jonathan W. Willett A1 Youngchang Kim A1 Ruiying Wu A1 Gyorgy Babnigg A1 Sean Crosson YR 2018 UL http://biorxiv.org/content/early/2018/01/22/251942.abstract AB The Brucella abortus general stress response sigma factor, σE1, directly and indirectly regulates the transcription of dozens of genes that influence stress survival and host infection. Characterizing the functions of σE1 regulated genes therefore contributes to understanding of B. abortus physiology and infection biology. Transcription of the IclR family regulator, Bab2_0215, is indirectly activated by σE1 but its function remains undefined. We present a structural and functional characterization of Bab2_0215, which we have named Brucella adipic acid activated regulator (BaaR). BaaR adopts a classic IclR-family fold and directly regulates the transcription of two operons with predicted roles in carboxylic acid oxidation. BaaR binds two sites on chromosome II between baaR and a divergently transcribed hydratase/dehydrogenase (acaD2), and represses transcription. We identified three carboxylic acids (adipic acid tetradecanedioic acid, ε-aminocaproic acid) and a lactone (ε-caprolactone) that enhance transcription from the baaR and acaD2 promoters. However, neither the activating acids nor caprolactone enhance transcription by binding directly to BaaR. Induction of baaR transcription by adipic acid requires the gene bab2_0213, which encodes a major facilitator superfamily transporter, suggesting that Bab2_0213 transports adipic acid across the inner membrane. We conclude that a set of structurally related organic molecules activate transcription of genes repressed by BaaR. Our study provides molecular-level understanding of a gene expression program regulated downstream of σE1.