The assembly of proteins is a universal biological process whose fundamental principles and machineries are conserved from bacteria to human. In the case of aberrant protein assembly, a cellular stress response is activated which, on one hand, elevates the expression of genes whose products assist in protein folding, assembly and degradation, and on the other, lowers protein synthesis to reduce the burden on the assembly machinery. Defects in these two highly conserved complementary responses can have broad consequences ranging from human diseases to loss of bacterial viability and virulence. This research investigates the assembly of [unreadable]-barrel outer membrane proteins (OMPs) in Escherichia coli. OMP assembly proceeds in two distinct phases, the first of which occurs in the soluble environment of the periplasm where nascent polypeptides attain folding status required for the second phase that occurs in the outer membrane where the final assembly and membrane insertion are achieved. More specifically, the proposed research will examine the role of YfgL, a lipoprotein component of the recently discovered OMP assembly machinery. The absence of YfgL confers pleiotropic phenotypes, including a significant delay in [unreadable]-barrel OMP assembly kinetics, conditional lethality in a background devoid of the major periplasmic protease DegP, drug hypersensitivity, and reduced virulence in E. coli and Salmonella typhimurium. Together, these phenotypes of YfgL mutants reflect broad and significant roles for YfgL in bacterial physiology and pathogenesis. The role of a novel protein, YqjB, in reducing envelope stress will also be examined. It is hypothesized that elevated YqjB levels under envelope stress conditions modulate the EnvZ/OmpR two-component regulatory system to reduce OMP synthesis, thereby relieving envelope stress. The two aims of this proposal are directed at gaining a deeper understanding of the mechanism by which the soluble OMP assembly events are coordinated with those that occur in the outer membrane and how the interconnected regulatory network help reduce envelope stress by down-regulating OMP synthesis. PUBLIC HEALTH RELEVANCE: The assembly of proteins is a universal biological process whose fundamental principles and machineries are conserved from bacteria to human. In the case of aberrant protein assembly, a cellular stress response is activated which, on one hand, elevates the expression of genes whose products assist in protein folding, assembly and degradation, and on the other, lowers protein synthesis to reduce the burden on the assembly machinery. Defects in these two highly conserved complementary responses can have broad consequences ranging from human diseases to loss of bacterial viability and virulence.