Altered bacteriophage lambda expression in cell division mutants capR(lon) of Escherichia coli K-12

Lon and ClpP proteases participate in the physiological disintegration of bacterial inclusion bodies

Aggregated protein is solubilized by the combined activity of chaperones ClpB, DnaK and small heat-shock proteins, and this could account, at least partially, for the physiological disintegration of bacterial inclusion bodies. In vivo, the involvement of proteases in this process had been suspected but not investigated. By using an aggregation prone beta-galactosidase fusion protein produced in Escherichia coli, we show in this study that the main ATP-dependent proteases Lon and ClpP participate in the physiological disintegration of cytoplasmic inclusion bodies, their absence minimizing the protein removal up to 40%. However, the role of these proteases is clearly distinguishable especially regarding the fate of solubilized protein. While Lon appears as a minor contributor in the disintegration process, ClpP directs an important attack on the released or releasable protein even not being irreversibly misfolded. ClpP is then observed as a wide-spectrum, main processor of aggregation-prone proteins and also of polypeptides physiologically released from inclusion bodies, even when occurring as soluble versions with a conformation compatible with their enzymatic activity.

Regulation of cell division in Escherichia coli: SOS induction and cellular location of the sulA protein, a key to lon-associated filamentation and death

Mutations in sulA (sfiA) block the filamentation and death of capR (lon) mutants that occur after treatments that either damage DNA or inhibit DNA replication and thereby induce the SOS response. Previous sulA-lacZ gene fusion studies showed that sulA is transcriptionally regulated by the SOS response system (lexA/recA). SulA protein has been hypothesized to be additionally regulated proteolytically through the capR (lon) protease, i.e., in lon mutants lacking a functional ATP-dependent protease there would be more SulA protein. A hypothesized function for SulA protein is an inhibitor of cell septation. To investigate aspects of this model, we attempted to construct lon, lon sulA, and lon sulB strains containing multicopy plasmids specifying the sulA+ gene. Multicopy sulA+ plasmids could not be established in lon strains because more SulA protein accumulates than in a lon+ strain. When the sulA gene was mutated by a mini Mu transposon the plasmid could be established in the lon strains. In contrast, sulA+ plasmids could be established in lon+, lon sulA, and lon sulB strains. The sulA+ plasmids caused lon sulA and lon sulB cells to exist as filaments without SOS induction and to be sensitive to UV light and nitrofurantoin. Evidence implicated higher basal levels of SulA protein in these lon plasmid sulA+ strains as the cause of filamentation. We confirmed that the SulA protein is an 18-kilodalton polypeptide and demonstrated that it was induced by treatment with nalidixic acid. The SulA protein was rapidly degraded in a lon+ strain, but was comparatively more stable in vivo in a lon sulB mutant. Furthermore, the SulA protein was localized to the membrane by several techniques.

DNA-stimulated ATPase activity on the lon (CapR) protein

The gene product of the pleiotropic lon (also called capR) locus in Escherichia coli, the CapR protein, is an ATP hydrolysis-dependent protease and a nonspecific nucleic acid-binding protein. We demonstrated that it is also a DNA-stimulated adenosine triphosphatase (ATPase). This new activity is distinct from the protease-associated ATPase activity and occurs in the absence of proteolytic substrate. The reaction requires the presence of a divalent cation and has a pH optimum of 8.0. The products of the reaction are ADP and inorganic phosphate. No adenylation or phosphorylation of the DNA or proteins was detected. The maximum rate of ATP hydrolysis occurs in the presence of supercoiled (form I) DNA. Relaxed circles (form II), double-stranded DNA, and single-stranded DNA are less effective in promoting ATPase activity, whereas RNA is inactive. The DNA-stimulated ATPase activity is inhibited by a mutationally altered form of the CapR protein called the CapR9 protein. The interaction of the CapR and CapR9 subunits suggests that this enzymatic activity of the CapR protein is oligomeric in the presence of DNA. Our in vitro experiments indicate a possible role for nucleic acids in the regulation of all lon (capR) activity.

Conservation of capR (lon) DNA of Escherichia coli K-12 between distantly related species

Mutations in the capR gene of Escherichia coli K-12 are responsible for a wide variety of phenotypic changes, including defects in cell division. Since this gene plays a critical role in cell division, it might be evolutionarily conserved. Of the DNAs examined by Southern analysis, capR probe sequences were found not only in other enterics but also in Caulobacter crescentus CB13 and the distantly related archebacterium Halobacterium halobium R1.

Escherichia coli polypeptide controlled by the lon (capR) ATP hydrolysis-dependent protease and possibly involved in cell division

Mutation in the gene lon (capR) of Escherichia coli K-12 causes conditional inhibition of cell division. Two-dimensional gel electrophoresis was used to compare polypeptides from isogenic capR+ and capR strains. One polypeptide was present in the capR strain but absent in the wild-type strain, and it was proteolyzed when the pure capR+ protease was added to the capR extract. This polypeptide could only be detected in the capR strain when cell division was inhibited, and its synthesis was independent of the SOS response.

ATP hydrolysis-dependent protease activity of the lon (capR) protein of Escherichia coli K-12

Mutations in the lon (capR) gene result in multiple phenotypes, one of which is the failure to degrade abnormal and normal proteins (Deg-). Previous work with partially purified preparations showed that the lon (capR) gene product is a 94,000-dalton polypeptide with an affinity for nucleic acids. The lon (capR) protein has now been highly purified and is demonstrated to have an ATP-dependent protease activity. The enzyme hydrolyzed 3H-labeled alpha-casein into trichloroacetic acid-soluble forms in Tris buffer containing Mg2+ and ATP. The reaction has a pH optimum of 8.5 and ATP was the preferred nucleotide. CTP and UTP could substitute for ATP (75% and 67%, respectively) but GTP, ADP, AMP, cyclic AMP, and PPi could not. Proteolysis by the lon (capR) protein required ATP hydrolysis. Nonhydrolyzable analogs of ATP and CTP did not promote casein cleavage. When low concentrations of ATP were used, proteolysis stopped as the ATP pool was depleted. Casein stimulated lon (capR) ATPase activity, and the products were ADP and inorganic phosphate in equimolar amounts. No protein kinase activity was detected. The DNA-binding activity, present in partially pure preparations, was retained in the purified protein. The gene product purified from a lon nonsense mutant that exhibits the Deg- phenotype (capR9), lacked both the ATP-dependent protease and ATPase activities, though it retained DNA-binding activity. Absence of an ATP-dependent protease activity could account for many of the pleiotropic effects observed in lon mutants.

Identification of the gene lon (capR) product as a 94-kilodalton polypeptide by cloning and deletion analysis

A mutation in the lon (capR) gene of Escherichia coli K-12 effects several phenotypic alterations in the mutant cell, such as overproduction of capsular polysaccharide and sensitivity to ultraviolet or ionizing radiation. A previously cloned 9.2-megadalton (Md) EcoRI fragment contained the capR+ gene and specified two polypeptides, 94 kilodaltons (K) and 67K. To provide evidence that the 94K polypeptide is the capR+ gene product, we constructed a capR+ plasmid pJMC40, having a 2.0-Md EcoRI-PstI fragment which codes only for the 94K polypeptide. Plasmids pJMC22 and pJMC30, having deletions of 0.7 and 0.8 Md, respectively, from one end of the 2.0-Md fragment, were also constructed. Each codes for a shortened stable polypeptide (from the 94K). Neither plasmid can confer the capR+ phenotype to capR mutants, confirming that the unaltered 94K polypeptide is the capR+ gene product. Plasmids pJMC51 and pJMC52 each have a deletion of 0.7 Md from the other end of the 2.0-Md fragment, differing only in the orientation of the remaining 1.3-Md fragment with respect to the cloning vehicle. They are nonfunctional with respect to capR+ and do not code for a common polypeptide from the 1.3-Md fragment. These data indicate that the fragments in pJMC22 and pJMC30, which both code for shortened 94K polypeptides, contain the promoter-operator region of the capR gene. The deletion plasmids were also used to map chromosomal capR mutations.

Cloning of gene lon (capR) of Escherichia coli K-12 and identification of polypeptides specified by the cloned deoxyribonucleic acid fragment

A mutation in the lon (capR) gene of Escherichia coli K-12 results in overproduction of capsular polysaccharide and increased sensitivity to ultraviolet and ionizing radiations. The lon (capR) gene deoxyribonucleic acid was cloned from a new F' factor. The new plasmids, designated pBZ201 and pBZ203, (i) contained an additional 8.2-megadalton (Md) EcoRI fragment that had the same mobility as one of the EcoRI fragments of the F', and (ii) conferred repression of capsular polysaccharide synthesis and repression of sensitivity to ultraviolet radiation in a bacterial transformation experiment with capR mutant recipient strains. A capR9 mutant plasmid, pBZ201M9, was also isolated and conferred expression of mucoidy and ultraviolet sensitivity to a capR(+) (lon(+)) strain, indicating that the capR9 allele was dominant. Plasmids pBZ201M80, pBZ201M9-INSA, and pBZ201M9-INSB were characterized by transformation as containing recessive capR mutant alleles. Heteroduplex analyses and agarose gel electrophoresis of restriction endonuclease digests of plasmid DNA preparations revealed that (i) pBZ201M9-INSA and pBZ201M9-INSB each contains a 0.5-Md insertion (probably IS1) in the cloned DNA fragment at the same site, and (ii) pBZ201 and pBZ203, both capR(+) plasmids, contain the same 8.2-Md fragment cloned in opposite orientations with respect to the cloning vehicle, pSC101. Plasmid-specified polypeptides were determined by using strain CSR603 maxicells containing each plasmid. Two new polypeptides were coded by the lon(+) (capR(+)) 8.2-Md DNA fragment: Z1, 94 kilodaltons (94K), and Z2, 67K. The maxicells containing recessive capR mutant plasmids were deficient only in synthesis of the 94K polypeptide, and the dominant (capR9) mutant plasmid specified 5 to 10 times more of the 94K polypeptide than the maxicells containing the capR(+) plasmid. Other data indicated that the capR9-specified "94K polypeptide" was not identical to the capR(+)-specified "94K polypeptide." Thus the altered mutant polypeptide was synthesized in increased quantities, suggesting a defective mode of autogenous regulation for the capR9 polypeptide and effective autogenous regulation of the capR(+) polypeptide.

Cloned DNA fragment specifying major outer membrane protein a in Escherichia coli K-12

Plasmid pMC44 is a recombinant plasmid that contains a 2-megadalton EcoRI fragment of Escherichia coli K-12 DNA joined to the cloning vehicle, pSC101. The polypeptides specified by plasmid pMC44 were identified and compared with those specified by pSC101 to determine those that are unique to pMC44. Three polypeptides specified by plasmid pMC44 were localized in the cell envelope fraction of minicells: a Sarkosyl-insoluble outer membrane polypeptide (designated M2), specified by the cloned 2-megadalton DNA fragment, and two Sarkosyl-soluble membrane polypeptides specified by the cloning plasmid pSC101. Bacteria containing plasmid pMC44 synthesized quantities of M2 approximately equal to the most abundant E. coli K-12 outer membrane protein. Evidence is presented that outer membrane polypeptide M2, specified by the recombinant plasmid pMC44, is the normal E. coli outer membrane protein designated protein a by Lugtenberg and 3b by Schnaitman.