RNA Thermometer-coordinated Assembly of the Yersinia Injectisome

The type III secretion system (T3SS) is indispensable for successful host cell infection by many Gram-negative pathogens. The molecular syringe delivers effector proteins that suppress the host immune response. Synthesis of T3SS components in Yersinia pseudotuberculosis relies on host body tempera-ture, which induces the RNA thermometer (RNAT)-controlled translation of lcrF coding for a virulence master regulator that activates transcription of the T3SS regulon. The assembly of the secretion machin-ery follows a strict coordinated succession referred to as outside-in assembly, in which the membrane ring complex and the export apparatus represent the nucleation points. Two components essential for the ini-tial assembly are YscJ and YscT. While YscJ connects the membrane ring complex with the export appa-ratus in the inner membrane, YscT is required for a functional export apparatus. Previous transcriptome-wide RNA structuromics data suggested the presence of unique intercistronic RNATs upstream of yscJ and yscT. Here, we show by reporter gene fusions that both upstream regions confer translational control. Moreover, we demonstrate the temperature-induced opening of the Shine-Dalgarno region, which facili-tates ribosome binding, by in vitro structure probing and toeprinting methods. Rationally designed ther-mostable RNAT variants of the yscJ and yscT thermometers confirmed their physiological relevance with respect to T3SS assembly and host infection. Since we have shown in a recent study that YopN, the gatekeeper of type III secretion, also is under RNAT control, it appears that the synthesis, assembly and functionality of the Yersinia T3S machinery is coordinated by RNA-based temperature sensors at multiple levels. (c) 2022 Elsevier Ltd. All rights reserved.

Automated summary

The type III secretion system (T3SS) is crucial for successful host cell infection by Gram-negative pathogens, and it is coordinated by RNA-based temperature sensors at multiple levels. Components such as YscJ and YscT play important roles in T3SS assembly, and their translation is temperature-dependent.