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A High Resolution Method to Monitor Phosphorylation-dependent Activation of IRF3
Published on: January 24, 2016
RNA type III secretion signals that require Hfq.
George S Niemann1, Roslyn N Brown, Ivy T Mushamiri
1Department of Microbiology and Immunology, Oregon Health and Science University, Portland, Oregon, USA.
Journal of Bacteriology
|February 12, 2013
Summary
Salmonella effector protein secretion relies on RNA signals within their leader sequences, with Hfq protein playing a key role in recognizing these signals for translocation into host cells.
Area of Science:
- Microbiology
- Molecular Biology
- Bacterial Pathogenesis
Background:
- Salmonella virulence depends on type III secretion systems (T3SS) delivering effector proteins into host cells.
- The secretion signal for these effectors is poorly understood, with N-terminal or RNA-encoded signals proposed.
- Identifying the precise secretion signal is crucial for understanding Salmonella pathogenesis.
Purpose of the Study:
- To identify the minimum sequence required for Salmonella effector protein translocation.
- To investigate the role of RNA sequences in the 5' untranslated leader of effector proteins.
- To determine the mechanism of signal recognition, including the involvement of host or bacterial proteins like Hfq.
Main Methods:
- Fusion of 5' untranslated leader sequences from 42 Salmonella effector proteins to a reporter gene (CyaA').
- Testing reporter translocation into J774 macrophages to identify functional secretion signals.
- Co-immunoprecipitation and pull-down assays to identify proteins binding to effector RNA, specifically gtgA RNA.
- Analysis of effector translocation in an hfq mutant strain of Salmonella.
Main Results:
- RNA sequences from five effector genes (gtgA, cigR, gogB, sseL, steD) were sufficient for reporter translocation.
- The Hfq protein was identified as a specific binder to gtgA RNA.
- Hfq was essential for the translocation of GtgA, GogB, and SseL, but not CigR or SteD.
- The Salmonella pathogenicity island 2 (SPI-2) T3SS apparatus assembly was independent of Hfq.
Conclusions:
- Salmonella effector protein secretion utilizes RNA-encoded signals located in the 5' untranslated leader sequences.
- The Hfq protein is involved in recognizing these RNA signals for the translocation of specific effectors.
- Hfq-RNA complexes likely play a significant role in the signal recognition mechanism for Salmonella effector secretion.
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