An essential regulatory function of the DnaK chaperone dictates the decision between proliferation and maintenance in Caulobacter crescentus

Autor: Schramm, Frederic D., Heinrich, Kristina, Thüring, Marietta, Bernhardt, Jörg, Jonas, Kristina
Jazyk: angličtina
Rok vydání: 2017
Předmět:
Transcription
Genetic
lcsh:QH426-470
Gene Expression
Sigma Factor
DNA replication
Research and Analysis Methods
Biochemistry
Suppressor Genes
Heat Shock Response
Caulobacter
ATP-Dependent Proteases
Bacterial Proteins
Gene Types
Caulobacter crescentus
Genetics
Gene Expression and Vector Techniques
HSP70 Heat-Shock Proteins
Amino Acid Sequence
Molecular Biology Techniques
Molecular Biology
Cellular Stress Responses
Molecular Biology Assays and Analysis Techniques
Bacteria
Organisms
Biology and Life Sciences
Proteins
Proteases
DNA
Cell Biology
DNA-Directed RNA Polymerases
Gene Expression Regulation
Bacterial
HSP40 Heat-Shock Proteins
Enzymes
Nucleic acids
lcsh:Genetics
Experimental Organism Systems
Cell Processes
Mutation
Enzymology
Prokaryotic Models
Hyperexpression Techniques
bacteria
Heat-Shock Response
Research Article
Molecular Chaperones
Transcription Factors
Zdroj: PLoS Genetics, Vol 13, Iss 12, p e1007148 (2017)
PLoS Genetics
ISSN: 1553-7404
1553-7390
Popis: Hsp70 chaperones are well known for their important functions in maintaining protein homeostasis during thermal stress conditions. In many bacteria the Hsp70 homolog DnaK is also required for growth in the absence of stress. The molecular reasons underlying Hsp70 essentiality remain in most cases unclear. Here, we demonstrate that DnaK is essential in the α-proteobacterium Caulobacter crescentus due to its regulatory function in gene expression. Using a suppressor screen we identified mutations that allow growth in the absence of DnaK. All mutations reduced the activity of the heat shock sigma factor σ32, demonstrating that the DnaK-dependent inactivation of σ32 is a growth requirement. While most mutations occurred in the rpoH gene encoding σ32, we also identified mutations affecting σ32 activity or stability in trans, providing important new insight into the regulatory mechanisms controlling σ32 activity. Most notably, we describe a mutation in the ATP dependent protease HslUV that induces rapid degradation of σ32, and a mutation leading to increased levels of the house keeping σ70 that outcompete σ32 for binding to the RNA polymerase. We demonstrate that σ32 inhibits growth and that its unrestrained activity leads to an extensive reprogramming of global gene expression, resulting in upregulation of repair and maintenance functions and downregulation of the growth-promoting functions of protein translation, DNA replication and certain metabolic processes. While this re-allocation from proliferative to maintenance functions could provide an advantage during heat stress, it leads to growth defects under favorable conditions. We conclude that Caulobacter has co-opted the DnaK chaperone system as an essential regulator of gene expression under conditions when its folding activity is dispensable.
Author summary Molecular chaperones of the Hsp70 family belong to the most conserved cellular machineries throughout the tree of life. These proteins play key roles in maintaining protein homeostasis, especially under heat stress conditions. In diverse bacteria the Hsp70 homolog DnaK is essential for growth even in the absence of stress. However, the molecular mechanisms underlying the essential nature of DnaK have in most cases not been studied. We found in the α-proteobacterium Caulobacter crescentus that the function of DnaK as a folding catalyst is dispensable in the absence of stress. Instead, its sole essential function under such conditions is to inhibit the activity of the heat shock sigma factor σ32. Our findings highlight that some bacteria have co-opted chaperones as essential regulators of gene expression under conditions when their folding activity is not required. Furthermore, our work illustrates that essential genes can perform different essential functions in discrete growth conditions.
Databáze: OpenAIRE
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