Phase Variation Sample Clauses

Phase Variation. Another mechanism of immune evasion is to alter the expression or composition of antigenic structures recognized by the host. Two large structures found on the P. mirabilis outer membrane which generate a humoral response in mice include fimbriae and flagella (61, 84). The MR/P fimbria are phase variable through a mechanism of site- specific inversion. The mrp operon, encoding the MR/P fimbria, is transcribed divergently from mrpI encoding the recombinase MrpI (85). The mrp operon is preceded by a σ70 promoter within an invertible repeat which is under MrpI control (85). When the σ70 promoter faces the mrp operon, the MR/P is phase ON. When the σ70 promoter faces mrpI, MR/P is phase OFF (51). The mrp promoter orientation is fixed in the absence of MrpI suggesting it is the sole recombinase for the operon (51). Another element affecting MR/P expression is the last gene in the mrp operon, mrpJ, which encodes a transcriptional regulator. MrpJ activates expression of the mrp operon promoting MR/P phase ON (86). Additionally, there are 14 paralogs of mrpJ in P. mirabilis: 10 paralogs are a part of fimbrial operons and 4 mrpJ paralogs are orphans (87). It is unknown if any of the MR/P paralogs or the other fimbrial systems in P. mirabilis are phase variable, but altering expression of any of these genes could contribute to fimbrial diversity and subsequent fitness within the host. The effect of the phase variable mrp operon is not limited to MR/P fimbriation as it extends to the repression of motility. Locking MR/P in phase OFF increases swarming motility (50), and artificial overexpression of 12 mrpJ paralogs thwarts motility to different degrees, with some paralogs preventing swarmer cell differentiation altogether (87). MrpJ and its paralog UcaJ directly bind upstream of the master flagellar operon, flhDC, mediating direct repression (88). The other mrpJ paralogs contain a conserved DNA-binding domain, but it is unknown if they can bind flhDC. Transcriptome profiling of P. mirabilis during urinary tract infection revealed the mrp genes are the most highly expressed during early infection (1-3 days) but their expression decreased in later infection (3-7 days). Flagellar genes were the most down-regulated genes in early infection, but in later stages of infection their expression increased (52). Overall, P. mirabilis is fervently committed to inversely expressing fimbriae and flagella. Altering the expression of these structures has implications for infection a...
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Related to Phase Variation

  • F3 Variation F3.1 The Authority may from time to time during the Contract Period, by written notice to the Contractor, request a variation of the Contract provided that such variation does not amount to a material change to it. Such a change is hereinafter called a “Variation”.

  • MODIFICATION & VARIATION The Company may, from time to time and at any time without notice to You, modify this Agreement. You agree that the Company has the right to modify this Agreement or revise anything contained herein. You further agree that all modifications to this Agreement are in full force and effect immediately upon posting on the Website and that modifications or variations will replace any prior version of this Agreement, unless prior versions are specifically referred to or incorporated into the latest modification or variation of this Agreement.

  • WAIVER AND VARIATION 13. No waiver or variation of this Parent Agreement shall be of any force unless such waiver or variation is agreed upon in writing and signed by an authorised representative of each of the Parties.

  • No Variation This Agreement cannot be amended or varied except in writing signed by the parties.

  • Construction Budget The total amount indicated by the District for the Project plus all other costs, including design, construction, administration, financing, and all other costs.

  • Variation No variation of this Agreement shall be effective unless it is in writing and signed by the parties (or their authorised representatives).

  • Modification of Budget Upon written approval of County, Subrecipient shall have the authority to transfer allocated program funds from one category of the overall program Budget to another category of the overall Budget. No such transfer may be made without the express prior written approval of County. A modification of the Budget may include the addition of any new Budget category.

  • Variation of the contract The parties undertake not to vary or modify the Clauses. This does not preclude the parties from adding clauses on business related issues where required as long as they do not contradict the Clause. Clause 11

  • Construction Schedule The progress schedule of construction of the Project as provided by Developer and approved by District.

  • Project Implementation 2. The Borrower shall:

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