Master's Theses

Date of Award

2015

Document Type

Thesis

Department

Biology

First Advisor

Anuradha Janakiraman

Second Advisor

Christine Li

Third Advisor

Shireen Saleque

Keywords

Bacteria, Cytokinesis, Proteolysis

Abstract

Cell division in bacteria requires the assembly of a macromolecular protein machinery at midcell that is spatiotemporally regulated during the bacterial cell cycle. Central to the process of division is the assembly of a cytokinetic ring-like structure, termed the Z-ring, formed by polymers of the essential tubulin-homolog FtsZ. Polymerization of FtsZ is regulated by a number of proteins that bind FtsZ and regulate its assembly/disassembly mechanisms. Despite being extensively studied, the molecular nature of the diverse protein-protein interactions that regulate the assembly of FtsZ during early stages of division is not well understood. Here, I focus on an FtsZ-ring stabilizer in E. coli – ZapC, which is conserved in a number of related Gram-negative bacteria and binds and bundles FtsZ in vitro. Strains with double mutations in zapC and another positive FtsZ-regulator display division defects indicating that ZapC promotes the integrity of the Z-ring in vivo. Recent evidence from our laboratory suggests that ZapC may be a substrate of the cellular protease ClpXP in E. coli. The conserved molecular chaperone ClpXP is responsible for degradation of a wide range of substrates, including FtsZ in E. coli. Here, we show that that ZapC and ClpX proteins interact in a bacterial two-hybrid (BACTH) assay. A zapC strain bearing a mutation in the putative ClpX recognition sequence is unable to interact with ClpX in a BACTH assay, suggesting that ZapC is a likely substrate of ClpXP. In addition, cell morphologies and viabilities of strains overexpressing or lacking ClpXP in wildtype or zapC mutant backgrounds show differences in cell lengths and viabilities, indicating that ClpX and ZapC act in the same functional pathway in division.

Available for download on Monday, January 01, 2018

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