Reference no: EM132486534

You identify a new Type XI secretion system (TXISS) in your favorite bacterium. It uses a hierarchical regulatory pathway (of Class I and Class II regulated promoters) to control expression of the components of the apparatus and for the secreted proteins. Class I promoters, which require sigma⁷⁰, are induced by exposure to high arsenic concentrations and control expression of genes encoding the proteins making up the TXISS apparatus. One additional Class I promoter also directs transcription of an operon that encodes two genes; one for an alternate sigma factor (SigZ, sigma ^Z) and another gene encoding a protein (GisZ) that carries the N-terminal secretion signal sequence for recognition by the TXISS apparatus. Class II promoters requires SigmaZ for expression and are only transcribed after the apparatus is fully assembled. Three Class II proteins (GisY, GisX, and GisW) each contain an N-terminal secretion signal sequences and are substrates of the TXISS. The gisY, gisX and gisW genes are not encoded in an operon. You have recently shown by cross-linking and co-immunoprecipitation that SigZ and GisZ proteins directly interact with one another.

Provide a simple regulatory model to explain the activation of Class II gene transcription by sigma^Z, which includes SigZ/GisZ interactions and timing of substrates via the TXISS. Include a diagram to show how your model works in the presence of arsenic