Structure and functional implications of WYL-domain-containing transcription factor PafBC involved in the mycobacterial DNA damage response

Abstract

In mycobacteria, transcriptional activator PafBC is responsible for upregulating the majority of genes induced by DNA damage. Understanding the mechanism of PafBC activation is impeded by a lack of structural information on this transcription factor that contains a widespread, but poorly understood WYL domain frequently encountered in bacterial transcription factors. Here, we determined the crystal structure of Arthrobacter aurescens PafBC. The protein consists of two modules, each harboring an N-terminal helix-turn-helix DNA binding domain followed by a central WYL and a C-terminal extension (WCX) domain. The WYL domains exhibit Sm-folds, while the WCX domains adopt ferredoxin-like folds, both characteristic for RNA binding proteins. Our results suggest a mechanism of regulation in which WYL domain-containing transcription factors may be activated by binding RNA molecules. Using an in vivo mutational screen in Mycobacterium smegmatis, we identify potential co-activator binding sites on PafBC.