FtsE and FtsX have homology to the ABC transporter superfamily of proteins and appear to be widely conserved among bacteria. Early work implicated FtsEX in cell division in Escherichia coli, but this was subsequently challenged, in part because the division defects in ftsEX mutants are often salt remedial. Strain RG60 has an ftsE::kan null mutation that is polar onto ftsX. RG60 is mildly filamentous when grown in standard Luria-Bertani medium (LB), which contains 1% NaCl, but upon shift to LB with no NaCl growth and division stop. We found that FtsN localizes to potential division sites, albeit poorly, in RG60 grown in LB with 1% NaCl. We also found that in wild-type E. coli both FtsE and FtsX localize to the division site. Localization of FtsX was studied in detail and appeared to require FtsZ, FtsA, and ZipA, but not the downstream division proteins FtsK, FtsQ, FtsL, and FtsI. Consistent with this, in media lacking salt, FtsA and ZipA localized independently of FtsEX, but the downstream proteins did not. Finally, in the absence of salt, cells depleted of FtsEX stopped dividing before any change in growth rate (mass increase) was apparent. We conclude that FtsEX participates directly in the process of cell division and is important for assembly or stability of the septal ring, especially in salt-free media.In Escherichia coli, the division septum forms via the coordinated inward growth of all three layers of the cell envelopethe cytoplasmic membrane, the peptidoglycan wall, and the outer membrane. To date, about a dozen E. coli genes are known to be specifically required for septation (3, 11). These genes share two important properties: (i) loss of function mutations result in the formation of long, aseptate filaments with regularly spaced nucleoids (the fts, or filamentation temperature-sensitive phenotype), and (ii) the proteins encoded by these genes localize to the division site. Because cell division genes are generally essential and because lesions in many housekeeping genes can affect cell division indirectly, there have not been any exhaustive screens for division mutants. Thus, it seems likely that more division genes remain to be described.A number of mutant hunts, starting with the pioneering work of Hirota and coworkers in the 1960s, suggested that there is an important cell division gene located at about 76 min on the E. coli chromosome (30). This locus was originally designated ftsE. One interesting property of ftsE mutants is that many are salt remedial, meaning that viability is restored by inclusion of NaCl in the growth medium. The amount of salt required for rescue is strain dependent, but generally in the range of 0.5%. Studies by Salmond and colleagues in the 1980s revealed that "ftsE" comprised two genes, which were then designated ftsE and ftsX (13). Moreover, the sequence of these genes revealed clear homology to ABC transporters; FtsE is the ATP-binding cassette (ABC) component, while FtsX is the membrane component. ABC transporters use energy from ATP to transport a wide variety of sub...

SummaryThe genes ftsE and ftsX are organized in one operon together with ftsY. FtsY codes for the receptor of the signal recognition particle (SRP) that functions in targeting a subset of inner membrane proteins. We have found no indications for a structural relationship between FtsE/X and FtsY. Evidence is presented that FtsE and FtsX form a complex in the inner membrane that bears the characteristics of an ATP-binding cassette (ABC)-type transporter. FtsE is a hydrophilic nucleotide-binding protein that has a tendency to dimerize and associates with the inner membrane through an interaction with the integral membrane protein FtsX. An FtsE null mutant showed filamentous growth and appeared viable on high salt medium only, indicating a role for FtsE in cell division and/or salt transport.

Chapter 1. Introduction General Introduction Dissertation Organization Literature Review A timeline of research begins with investigators at the Institut Pasteur A putative cold-sensitive mutant of ftsE Important work on ftsE in the United Kingdom: 1980s ftsE questioned as a cell division gene Cell division, transport, and now flagella: The list of pleiotropies grows Regulation of the ftsYEX operon and more important work in the United Kingdom: 1990's The focus of the operon becomes ftsY, the SRP docking protein homologue Beyond ftsY, the homologies offtsE and ftsX: E. coli genetics applied to other systems Regulation revisited A possible explanation for the pleiotropic phenotype of an ftsE mutant: A unifying hypothesis A comprehensive characterization offtsEX The global picture Literature Cited Chapter 2. Characterization of a null mutant of ftsE of Escherichia coli Introduction Materials and Methods 52 Results 54 Discussion 71 Literature Cited 74 V Chapter 3. Phumid shuffling system for the isolation of temperature-sensitive mutants in essential genes of Escherichia coli Introduction Materials and Methods 78 Results and Disussion 80 Literature Cited 88 Chapter 4. Cell division septation machinery intact in a filamented ftsE'. :kanl null mutant of Escherichia coli 89 Introduction 89 Materials and Methods 91 Results 93 Discussion 107 Literature Cited 109 Chapter 5. A cold-senstive mutant of ftsX of Escherichia coli revisited 110 Introduction 110 Materials and Methods 111 Results and Discussion 113 Literature Cited 117 Chapter 6. General Conclusions 118