AUTHOR=Oh Yuna , Song Su-Yeon , Kim Hye-Jun , Han Gil , Hwang Jihwan , Kang Ho-Young , Oh Jeong-Il 

TITLE=The Partner Switching System of the SigF Sigma Factor in Mycobacterium smegmatis and Induction of the SigF Regulon Under Respiration-Inhibitory Conditions

JOURNAL=Frontiers in Microbiology

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.588487

DOI=10.3389/fmicb.2020.588487

ISSN=1664-302X

ABSTRACT=<p>The partner switching system (PSS) of the SigF regulatory pathway in <italic>Mycobacterium smegmatis</italic> has been previously demonstrated to include the anti-sigma factor RsbW (MSMEG_1803) and two anti-sigma factor antagonists RsfA and RsfB. In this study, we further characterized two additional RsbW homologs and revealed the distinct roles of three RsbW homologs [RsbW1 (MSMEG_1803), RsbW2 (MSMEG_6129), and RsbW3 (MSMEG_1787)] in the SigF PSS. RsbW1 and RsbW2 serve as the anti-sigma factor of SigF and the protein kinase phosphorylating RsfB, respectively, while RsbW3 functions as an anti-SigF antagonist through its protein interaction with RsbW1. Using relevant mutant strains, RsfB was demonstrated to be the major anti-SigF antagonist in <italic>M. smegmatis</italic>. The phosphorylation state of Ser-63 was shown to determine the functionality of RsfB as an anti-SigF antagonist. RsbW2 was demonstrated to be the only protein kinase that phosphorylates RsfB in <italic>M. smegmatis</italic>. Phosphorylation of Ser-63 inactivates RsfB to render it unable to interact with RsbW1. Our comparative RNA sequencing analysis of the wild-type strain of <italic>M. smegmatis</italic> and its isogenic Δ<italic>aa</italic><sub>3</sub> mutant strain lacking the <italic>aa</italic><sub>3</sub> cytochrome <italic>c</italic> oxidase of the respiratory electron transport chain revealed that expression of the SigF regulon is strongly induced under respiration-inhibitory conditions in an RsfB-dependent way.</p>