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The flagellar-specific transcription factor, σ 28 , is the Type III secretion chaperone for the flagellar-specific anti-σ 28 factor FlgM

2006; Cold Spring Harbor Laboratory Press; Volume: 20; Issue: 16 Linguagem: Inglês

10.1101/gad.380406

1549-5477

Phillip D. Aldridge, Joyce E. Karlinsey, Christine Aldridge, Christopher Birchall, Danielle Thompson, Jin Yagasaki, Kelly T. Hughes,

Escherichia coli research studies

The σ 28 protein is a member of the bacterial σ 70 -family of transcription factors that directs RNA polymerase to flagellar late (class 3) promoters. The σ 28 protein is regulated in response to flagellar assembly by the anti-σ 28 factor FlgM. FlgM inhibits σ 28 -dependent transcription of genes whose products are needed late in assembly until the flagellar basal motor structure, the hook-basal body (HBB), is constructed. A second function for the σ 28 transcription factor has been discovered: σ 28 facilitates the secretion of FlgM through the HBB, acting as the FlgM Type III secretion chaperone. Transcription-specific mutants in σ 28 were isolated that remained competent for FlgM-facilitated secretion separating the transcription and secretion-facilitation activities of σ 28 . Conversely, we also describe the isolation of mutants in σ 28 that are specific for FlgM-facilitated secretion. The data demonstrate that σ 28 is the Type III secretion chaperone for its own anti-sigma factor FlgM. Thus, a novel role for a σ 70 -family transcription factor is described.