bioRxiv2018
Though bacteria in nature are often nutritionally limited and growing slowly, most of our understanding of core cellular processes such as transcription comes from studies in a handful of model organisms doubling rapidly under nutrient-replete conditions. We previously identified a small protein of unknown function, called SutA, in a global screen of proteins synthesized in Pseudomonas aeruginosa under growth arrest (Babin BM, et al. (2016) SutA is a bacterial transcription factor expressed during slow growth in Pseudomonas aeruginosa. PNAS 113(5):E597-605). SutA binds RNA polymerase (RNAP), causing widespread changes in gene expression, including upregulation of the ribosomal RNA (rRNA) genes. Here, using biochemical and structural methods, we examine how SutA interacts with RNAP and the functional consequences of these interactions. We show that SutA consists of a central -helix with unstructured N- and C-terminal tails, and binds to the {beta}1 domain of RNAP. It activates transcription from the P. aeruginosa rrn promoter by both the housekeeping sigma factor holoenzyme (E{sigma}70) and the general stress response sigma factor holoenzyme (E{sigma}S) in vitro, and its N-terminal tail is required for activation in both holoenzyme contexts. However, we find that the interaction between SutA and each holoenzyme is distinct, with the SutA C-terminal tail and an acidic loop unique to {sigma}70 playing the determining roles in these differences. Our results add SutA to a growing list of transcription regulators that use their intrinsically disordered regions to remodel transcription complexes.\n\nSIGNIFICANCELittle is known about how bacteria regulate their activities during periods of dormancy, yet growth arrest dominates bacterial existence in most environments and is directly relevant to the problem of physiological antibiotic tolerance. Though much is known about transcription in the model organism, Escherichia coli, even there, our understanding of gene expression during dormancy is incomplete. Here we explore how transcription under growth arrest is modulated in Pseudomonas aeruginosa by the small acidic protein, SutA. We show that SutA binds to RNA polymerase and controls transcription by a mechanism that is distinct from other known regulators. Our work underscores the potential for fundamental, mechanistic discovery in this important and understudied realm of bacterial physiology.