Protein degradation in Escherichia coli: the lon gene controls the stability of sulA protein.

Abstract

Escherichia coli Ion mutants are defective in the ATP-dependent proteolysis of abnormal proteins. The mutants are also sensitive to ultraviolet light (UV) in that septation is inhibited after exposure to UV. sulA mutations, isolated as suppressors of UV sensitivity unlinked to ion, do not affect proteolysis but allow septation to occur after DNA damage. We have confirmed the hypothesis that the product ofthe sulA gene is degraded by ion proteolysis. If sulA (the product of sulA) is a UV-inducible division inhibitor, as suggested by a variety of experiments, lon (the product of ion) may regulate cell division by regulating the half-life of sulA. We cloned the sulA gene in a bacteriophage A vector from a plasmid carrying the ompA region ofE. coli. An 18-kilodalton polypeptide was identified as the product of the sulA gene. Pulse-chase labeling demonstrated that the half-life of the sulA protein is 1.2 min in ion' cells and 19 min in Ion-cells. This work demonstrates that lon proteolysis affects the stability of a native E. coli protein.The ion mutations of Escherichia coli affect a variety of physiological processes. Ion mutants have decreased ability to degrade abnormal proteins (1-4), overproduce capsular polysaccharide (5), and are defective for lysogeny of bacteriophages A and P1 (6, 7). They are also sensitive to DNA-damaging agents, such as ultraviolet light (UV) or methyl methanesulfonate (MeMes) (8). This UV sensitivity seems to result from an exaggeration of the normal inhibition of E. coli cell division after DNA damage (9). Ion mutants do not recover from this division arrest and are therefore UV and MeMes sensitive.Mutations identified in ion strains as suppressors of sensitivity to UV or MeMes map at two loci, sulA and sulB. These suppressors block the lethal filamentation seen in ion strains but do not affect other ion phenotypes (10-14). sulA and sulB also do not affect the cell's UV repair system or its induction. George and her co-workers (15) proposed that a division inhibitor, in-

Lon protease promotes survival of Escherichia coli during anaerobic glucose starvation

“…In E. coli, Lon is involved in the degradation of abnormal and misfolded proteins (Chung and Goldberg, 1981;Laskowska et al, 1996;Rosen et al, 2002). It also degrades certain regulatory proteins, including the SulA cell division regulator (Mizusawa and Gottesman, 1983;Schoemaker et al, 1984;Higashitani et al, 1997), the positive regulator of capsule synthesis, RcsA (Torres-Cabassa and Gottesman, 1987), and possibly TER components involved in blocking septation sites during the SOS response (Dopazo et al, 1987). Lon is also involved in the turnover of several antitoxin proteins in toxin-antitoxin systems (Gerdes, 2000).…”

Identification of the Proteasome Inhibitor MG262 as a Potent ATP-Dependent Inhibitor of the Salmonella enterica serovar Typhimurium Lon Protease

“…Homologs exist ubiquitously in nature, however they localize to the cytosol in prokaryotes and to the mitochondrial matrix in eukaryotes (8,15,16 (11,(18)(19)(20)(21)(22)(23).…”

“…In fact the E. coli and S. Typhimurium Lon proteases differ in only 3 amino acids, none of which occur within the functional domains of the enzyme, indicating the two may function comparably. This is supported by the fact that Lon-deficient E. coli and S. Typhimurium are indistinguishable in their increased sensitivity to UV light and other DNA damaging agents, as well as their decreased ability to degrade abnormal proteins (11,(18)(19)(20)(21)(22)(23).…”

Adaptor-mediated Lon proteolysis restrictsBacillus subtilishyperflagellation

“…Lon is thought to degrade misfolded proteins by recognizing hydrophobic peptide sequences known as degrons that are normally buried in the hydrophobic core of folded proteins and become solvent exposed upon protein misfolding (12,13). Lon is also known to conduct regulatory proteolysis by highly specific degradation of key cellular regulators but to date, little has been reported regarding Lon-specific adaptor proteins (10,(14)(15)(16)(17). Thus, if and how Lon distinguishes specific regulatory targets from general misfolded proteins is an open question.…”