Nucleotide sequence of the lspA gene, the structural gene for lipoprotein signal peptidase of Escherichia coli

The nucleotide sequence of the lspA gene coding for lipoprotein signal peptidase of Escherichia coli was determined and the amino acid sequence of the peptidase was deduced from it. The molecular mass and amino acid composition of the predicted lipoprotein signal peptidase were consistent with those of the signal peptidase purified from cells harboring the lspA gene-carrying plasmid. The peptidase most probably has no cleavable signal peptide. The lspA gene was preceded by the ileS gene coding for isoleucyl-tRNA synthetase and the tandem termination codons of the ileS gene overlapped with the initiation codon of the lspA gene.

The gene coding for lipoprotein signal peptidase (lspA) and that for isoleucyl-tRNA synthetase (ileS) constitute a cotranscriptional unit in Escherichia coli

The lspA gene coding for lipoprotein signal peptidase is located very close to the ileS gene coding for isoleucyl-tRNA synthetase on the Escherichia coli chromosome. Deletions were generated in vitro from both ends of the 4.3 kb fragment that carries the lspA gene and the ileS gene, and the expression of the two genes was examined before and after insertion of the trp promoter-operator at one end. The results indicate that the lspA and ileS genes constitute a cotranscriptional unit in the order of promoter- ileS - lspA . The gene order of dnaJ - rpsT - ileS - lspA - dapB around 0.5 min on the E. coli chromosome map was also determined.

Promoter exchange between ompF and ompC, genes for osmoregulated major outer membrane proteins of Escherichia coli K-12

Expression of the ompF and ompC genes coding for major outer membrane proteins OmpF and OmpC is regulated in opposite directions by medium osmolarity. Chimera genes were constructed by a reciprocal exchange of the promoter-signal sequence region between the two genes. The chimera gene construction was designed so that the proteins synthesized by these genes were essentially the same as the OmpC and OmpF proteins. Studies with the chimera genes demonstrated that the osmoregulation of the OmpF-OmpC synthesis was promoter dependent. They also showed that cells grew normally even when the osmoregulation took place in opposite directions. The effects of the ompR2 and envZ mutations, which suppress ompC and ompF expression, respectively, also became reversed. The reduced expression was still subject to the promoter-controlled osmoregulation. Based on these observations, the mechanism of regulation of the ompF-ompC gene expression and its physiological importance are discussed.

Mechanism of localization of major outer membrane lipoprotein in Escherichia coli. Studies with the OmpF-lipoprotein hybrid protein

A chimera gene consisting of the ompF promoter, the coding regions for the signal peptide and the NH2-terminal 11 amino acid residues of outer membrane OmpF protein, and the coding region for the major outer membrane lipoprotein devoid of the NH2-terminal 7 amino acid residues was constructed. Escherichia coli carrying the cloned chimera gene produced a hybrid protein with the predicted chemical structure. The protein was localized in the periplasmic space with an interaction with the peptidoglycan layer. These results indicate that the hybrid protein was expressed, secreted across the cytoplasmic membrane, and processed for the signal peptide normally. The hybrid protein, however, was not incorporated into the outer membrane, suggesting the importance of the lipid domain in the assembly of the lipoprotein into the outer membrane. Although a larger part of the protein was extractable with sodium dodecyl sulfate, a part of the hybrid protein was covalently bound to the peptidoglycan layer as the lipoprotein is. Upon treatment with lysozyme of the envelope the hybrid protein became water soluble. The solubilized protein most probably existed as a trimer. These results most likely suggest that the major lipoprotein exists as a trimer in the periplasmic space with interactions with the peptidoglycan layer through the protein domain on one side and with the outer membrane through the lipid domain on the other side.

The major outer membrane lipoprotein and new lipoproteins share a common signal peptidase that exists in the cytoplasmic membrane of Escherichia coli

The cell envelope of Escherichia coli possesses several lipoproteins including the major outer membrane lipoprotein. These lipoproteins are synthesized as a signal peptide-carrying precursor that is subsequently modified with glyceride. In this work, lipoprotein signal peptidase that processes the precursor of the major lipoprotein was partially purified from cells harboring a plasmid that carries the gene for this enzyme (1spA). The enzyme was also active against the glyceride-containing precursors of the peptidoglycan-associated lipoprotein and many additional membrane lipoproteins. The unmodified precursor of the major lipoprotein was not attacked by the enzyme. The enzyme was exclusively localized in the cytoplasmic membrane.

Post-translational modification and processing of outer membrane prolipoproteins in Escherichia coli

This mini review is primarily concerned with the biosynthesis of the major outer membrane lipoprotein of Escherichia coli. The lipoprotein is composed of fifty-eight amino acid residues, one glyceride residue and one acyl residue being at the amino terminal cysteine residue. About one-third of the lipoprotein is covalently bound to the underlying peptidoglycan layer and plays an important role in the assembly of the outer membrane on the peptidoglycan layer. The lipoprotein is first synthesized on ribosomes as a precursor form having twenty extra amino acid residues (signal peptide) at the amino terminus. During secretion through the cytoplasmic membrane, the modification at the cysteine residue that is to be the amino terminus of the mature lipoprotein and cleavage of the signal peptide take place successively. These events are then followed by N-acetylation of the terminal cysteine residue, translocation to the outer membrane, and covalent binding to the peptidoglycan layer of the lipoprotein. Digestion of the cleaved signal peptide also takes place upon cleavage of the signal peptide. In this review these chemical and topographical events are discussed step by step especially in relation to the process of protein secretion across the cytoplasmic membrane.

Outer membrane porins are important in maintenance of the surface structure of Escherichia coli cells

Escherichia coli cells lacking the OmpF and OmpC proteins, porin proteins of the outer membrane, are often unstable and easily revert to strains which either have regained one or both of these proteins or contain a new outer membrane protein. The structural importance of porin proteins in the cell surface was studied in the present work. Tris-hydrochloride buffer at a concentration of 120 mM caused deformation of the cell surface of a strain lacking these porins; the undulated appearance of the negatively stained cell surface changed to a smooth and expanded form. The Tris-induced deformation was seldom observed with either the wild-type strain or a pseudorevertant that possessed the OmpF protein. The role of the OmpF protein in stabilizing the cell surface against Tris treatment could be slightly taken over by the LamB protein, which shares a number of unique properties with the former proteins. The deformation of the cell surface by Tris-hydrochloride buffer was accompanied by a loss of viability, the lethal damage being especially significant when the cells lacked porins. Upon induction with maltose, cells with the undulated appearance could absorb lambda phages, whereas the deformed cells could not. These results suggest that the instability of cells lacking porins is primarily due to a structural defect of the outer membrane.

Genetic characterization of a gene for prolipoprotein signal peptidase in Escherichia coli

A mutation (lspA, prolipoprotein signal peptidase) rendering the prolipoprotein signal peptidase temperature-sensitive in Escherichia coli has been analyzed. The mutation was mapped in the dnaJ-rpsT-ileS-dapB region by interrupted mating with various Hfr strains and P1 phage transduction. lambda transducing phage lambda ddapB2 that carries the rpsT-ileS-dapB region was shown to complement the lspA mutation. Plasmid pLC3-13 which had been isolated from Clarke and Carbon's collection as a plasmid carrying the lspA locus was shown to carry the dnaJ and rpsT loci. Complementation analysis with plasmids carrying various DNA fragments derived from pLC3-13 showed that the lspA locus is between the rpsT and ileS loci. The wildtype allele was dominant over the lspA allele.

Mutation causing overproduction of outer membrane protein OmpF and suppression of OmpC synthesis in Escherichia coli

A novel mutation affecting the synthesis of major outer membrane proteins OmpF and OmpC in Escherichia coli K-12 is described. The mutation resulted in overproduction of the OmpF protein with concomitant suppression of OmpC synthesis. This mutation, designated as ompFp100, was mapped at 21 min on the E. coli chromosome map with the gene order aroA-aspC-ompF4-ompFp100-asnS-pyrD. This mutation was cis-dominant to the expression of the ompF gene. In addition, the direction of the mRNA transcription of the ompF gene was from asnS to aspC. These results strongly indicate that ompFp100 is a promoter mutation of the ompF gene. Introduction of an ompF mutation, which causes the disappearance of the OmpF protein, into strains carrying the ompFp100 mutation resulted in the reappearance of the OmpC protein in the outer membrane. Addition of a high concentration of sucrose to the medium, which suppresses the OmpF synthesis and stimulates the OmpC synthesis in the wild-type strain, resulted in the reappearance of the OmpC protein in the ompFp100 mutant with concomitant suppression of the overproduction of the OmpF protein. These results suggest that suppression of OmpC synthesis in the ompFp100 mutant is due to overproduction of the OmpF protein.

Cloning and expression of a gene coding for the prolipoprotein signal peptidase of Escherichia coli

An Escherichia coli mutant, Y815, has a temperature-sensitive prolipoprotein signal peptidase. IPTG-induced synthesis of the major outer membrane prolipoprotein (PLP) results in the inhibition of cell growth because of accumulation of PLP in its envelope [J. Bacteriol. (1982) 152, 1163-1168]. The 2000 E. coli strains of Clarke and Carbon's collection were screened for the presence of a plasmid complementing the IPTG-sensitivity of the growth of Y815. One plasmid, pLC3-13, complemented the IPTG-sensitivity. The envelope fraction prepared from Y815 transformed by pLC3-13 showed high activity of the PLP signal peptidase in vitro at high temperature. A 4 kb AccI fragment subcloned onto plasmid pHY001 was shown to carry the gene for the PLP signal peptidase.

DNA injection during bacteriophage T4 infection of Escherichia coli

The process of phage T4 DNA injection into the host cell was studied under a fluorescent microscope, using 4',6-diamidino-2-phenylindole as a DNA-specific fluorochrome. The phage DNA injection was observed when spheroplasts were infected with the artificially contracted phage particles having a protruding core. The DNA injection was mediated by the interaction of the core tip with the cytoplasmic membrane of the spheroplast. A membrane potential was not required for the process of DNA injection. On the other hand, DNA injection upon infection by intact noncontracted phage of the intact host cell was inhibited by an energy poison. Based on these observations, together with results from previous work, a model for the T4 infection process is presented, and the role of the membrane potential in the infection process is discussed.

Regulation of outer membrane porin protein synthesis in Escherichia coli K-12: ompF regulates the expression of ompC

The relative amounts of the OmpF and OmpC proteins in the outer membrane of Escherichia coli K-12 are affected differentially by high concentrations of substances like sucrose in culture media in such a manner that a decrease in the amount of the OmpF protein appears to be compensated for by a reciprocal increase in the OmpC protein. When an ompF mutation was introduced, OmpC synthesis became almost independent of sucrose and occurred at the fully induced level even in the absence of sucrose. On the other hand, introduction of an ompC mutation did not affect the sucrose-dependent profile of OmpF synthesis. The effect of the ompF mutation was also examined with the ompC-lac fusion strain, in which expression of beta-galactosidase is under the control of the ompC promoter. The expression of beta-galactosidase coded for by the ompC-lac fusion in the ompF+ and ompF- strains was essentially the same as that of the OmpC protein, being sucrose dependent in the ompF+ strain and sucrose-independent in the ompF mutant. From these results we conclude that sucrose in the medium primarily regulates ompF gene expression, which in turn regulates ompC gene expression at the transcriptional level. This sequential regulatory mechanism is discussed in relation to the function of the ompB locus.

Abnormal protein and lipid compositions of the cerebral myelin of a patient with maple syrup urine disease

Biochemical analyses were performed on the myelin isolated from the brain tissue of a patient with maple syrup urine disease. He was mostly treated by dietary management from day 8 after his birth until he died at 4 years and 5 months of age. It was found that the myelin contained major proteolipid-protein and high molecular weight protein and a very minor basic protein. The lipid composition of the myelin showed a marked decrease in phosphatidylethanolamine, but there was no remarkable reduction of cerebroside and sulfatide as well as other phospholipids in the myelin. Although the ganglioside composition of the myelin indicated that GM1 was a major ganglioside just like in the normal myelin, the myelin had an abnormal composition of an higher proportion of GD3 and a lower proportion of GM4, GD1b and GT1b. However, overall fatty acid compositions of the myelin lipids seemed rather normal.

Signal peptide digestion in Escherichia coli. Effect of protease inhibitors on hydrolysis of the cleaved signal peptide of the major outer-membrane lipoprotein

Upon incubation of the envelope fraction of Escherichia coli a precursor of the major outer membrane lipoprotein that accumulates in the cytoplasmic membrane of the globomycin-treated cell is processed to the mature form [Hussain, M., Ichihara, S., and Mizushima, S. (1980) J. Biol. Chem. 255, 3707-3712; (1982) J. Biol. Chem. 257, 5177-5182]. When this precursor-containing envelope fraction was incubated in the presence of protease inhibitors such as antipain, leupeptin, chymostatin and elastatinal, a new peptide appeared on a polyacrylamide gel at the position where the signal peptide was expected to appear. This was proved to be the signal peptide of the lipoprotein from the following facts: (a) its appearance is in proportion to the appearance of the lipoprotein and disappearance of the precursor; (b) when the cleavage of the signal peptide from the precursor was inhibited by globomycin, the peptide did not appear on the gel; and (c) the results of labeling of the peptide with [3H]leucine, [35S]methionine and [3H]arginine were consistent with the amino acid composition of the signal peptide. The signal peptide thus accumulated in the envelope fraction was hydrolyzed by an enzyme named 'signal peptide peptidase' when the envelope fraction was washed to remove the inhibitors. The hydrolysis was inhibited by re-addition of these inhibitors. The signal peptide peptidase hydrolyzed the signal peptide only after its cleavage from the lipoprotein precursor.

Primary structure of the ompF gene that codes for a major outer membrane protein of Escherichia coli K-12

The nucleotide sequence of the ompF gene coding for a major outer membrane protein of Escherichia coli K-12 has been determined and the amino acid sequence of the OmpF protein was deduced from it. The OmpF protein contains 340 amino acid residues, and is produced from a precursor having 22 extra amino acid residues, the signal peptide, at the amino terminus. The expected secondary structure of the OmpF protein had a high beta-sheet content with a low alpha-helix content. The promoter region and the transcription termination region of the ompF gene had a significantly high AT content, while the AT content of the coding region was about the same as the average AT content of the E. coli chromosome. Following the termination codon, a typical rho-independent transcription termination signal was observed. The codon usage in the ompF gene was highly nonrandom; the codons preferably utilized are those recognized by the most abundant species of isoaccepting tRNAs or those, among synonymous codons recognized by the same tRNA, that can interact more properly with the anticodon.

Roles of lipopolysaccharide and outer membrane protein OmpC of Escherichia coli K-12 in the receptor function for bacteriophage T4

The roles of lipopolysaccharide and OmpC, a major outer membrane protein, in the receptor function for bacteriophage T4 were studied by using Escherichia coli K-12 strains having mutations in the ompC gene or in genes controlling different stages of lipopolysaccharide synthesis. The receptor activity for T4 was monitored by (i) T4 sensitivity of intact cells, (ii) phage inactivation activity of cell envelopes, and (iii) phage inactivation activity of specimens reconstituted from purified OmpC and lipopolysaccharide. It was found that (i) in the presence of the OmpC protein, the essential region of the lipopolysaccharide for the receptor activity was the core-lipid A region that includes the heptose region, whereas the glucose region was not necessarily required for the receptor function; (ii) the OmpC protein was not required at all when the distal end of the lipopolysaccharide was removed to expose a glucose residue at the distal end; and (iii) when cells lacked both the OmpC protein and the glucose region, they became extremely resistant to T4. Based on these findings, the roles of the OmpC protein and lipopolysaccharide in T4 infection are discussed.

Mechanism of signal peptide cleavage in the biosynthesis of the major lipoprotein of the Escherichia coli outer membrane

On treatment of Escherichia coli cells with globomycin, a glyceride-containing precursor of the major outer membrane lipoprotein accumulates in the cytoplasmic membrane (Hussain, M., Ichihara, S., and Mizushima, S. (1980) J. Biol. Chem. 255, 3707-3712). When the envelope fraction from such cells was incubated in a suitable buffer, this precursor could be processed to the mature lipoprotein. The processing involved removal of the signal peptide and subsequent acylation of the NH2 terminus thus bared. Two types of peptidase and an acylation enzyme(s) were found to be involved in these processes. The enzyme that cleaves the signal peptide, called signal peptidase in this paper, had many unique properties: being highly resistant to high temperature, having a wide optimum pH range, and being highly sensitive to detergents. The other peptidase(s), called signal peptide peptidase in this paper, was assumed to be responsible for the digestion of the signal peptide that had been cleaved from the precursor lipoprotein. This enzyme was rather heat-sensitive. Thus the processing from the precursor to the mature lipoprotein at a high temperature resulted in accumulation of a peptide that was most probably the intact signal peptide. The third enzyme(s) involved in the processing was the one that is responsible for acylation of the newly bared NH2 terminus of the lipoprotein. The enzyme activity was also lost at 80 degrees C. In the light of these findings, the biosynthetic pathway of the lipoprotein is discussed.

Roles of cell surface components of Escherichia coli K-12 in bacteriophage T4 infection: interaction of tail core with phospholipids

The cell surface of Escherichia coli K-12, reconstituted from the OmpC protein, lipopolysaccharide, and the peptidoglycan layer, was active as a receptor for phage T4, resulting in the contraction of the tail sheath and the penetration of the core through the cell surface (Furukawa et al., J. Bacteriol. 140:1071--1080, 1979). In the present work the process of DNA ejection from the contracted T4 phage particle was studied. Contracted phage particles were adsorbed to phospholipid liposomes by the core tip. This adsorption resulted in ejection of phage DNA. Either phosphatidylglycerol or cardiolipin was active for the DNA ejection. A proton motive force across the liposome membrane was not required for these processes. The process of DNA ejection, however, was temperature dependent, whereas the adsorption of the core tip to liposomes took place at 4 degrees C. Based on these observations together with those in the previous paper, the process of T4 infection of E. coli K-12 cells is discussed with special reference to the roles of cell surface components.

Mechanism of export of outer membrane lipoproteins through the cytoplasmic membrane in Escherichia coli. Binding of lipoprotein precursors to the peptidoglycan layer

Upon treatment of Escherichia coli cells with globomycin, precursors of Braun's lipoprotein, a peptidoglycan-associated lipoprotein (PAL) and several new species of lipoproteins accumulated in the cell envelope (Hussain, M. Ichihara, S., and Mizushima, S. (1980) J. Biol. Chem. 255, 3707-3012; and Ichihara, S., Hussain, M., and Mizushima, S. (1981) J. Biol. Chem. 256, 3125-3129). The precursors of the Braun's lipoprotein and PAL thus accumulated were able to interact with the peptidoglycan layer. A considerable fraction of the precursor of Braun's lipoprotein was covalently bound to the peptidoglycan layer through its COOH-terminal lysine residue in the same manner as in the mature form. The manner of interaction of the precursor of PAL with the peptidoglycan layer was also the same as that of its mature form in which the central to COOH-terminal region of the lipoprotein is important for the interaction. Both precursors were localized in the cytoplasmic membrane when the outer and cytoplasmic membranes were separated after digestion by lysozyme of the peptidoglycan layer. When the cell envelope fraction was incubated, these precursors were chased to the corresponding mature forms. These results indicate that these proteins can be exported through the cytoplasmic membrane while they still retain the signal peptide that is most probably held in the cytoplasmic membrane.

Arrangement of bacteriophage lambda receptor protein (LamB) in the Escherichia coli cell surface

The lambda receptor protein (LamB) was assembled into an ordered hexagonal lattice structure with a lattice constant of about 7.8 nm in the presence of lipopolysaccharide. Both the heptose-containing polysaccharide region and the fatty acid region are suggested to be involved in the interaction with LamB. The lattice structure was preferably formed on the peptidoglycan layer when the lipoprotein was covalently bound to this layer. In the presence of chloroform, the ordered hexagonal lattice structure was active in the receptor function for lambda, resulting in phage adsorption and DNA ejection.

Role of lipopolysaccharide in the receptor function for bacteriophage TuIb in Escherichia coli

Bacteriophage TuIb required lipopolysaccharide in addition to the OmpC trimer as a receptor component. Both the fatty acid and polysaccharide regions of lipopolysaccharide were shown to participate in the receptor function. The roles of lipopolysaccharide and outer membrane proteins in the receptor function for T-even type bacteriophages are discussed.

Arrangement of bacteriophage lambda receptor protein (LamB) in the cell surface of Escherichia coli: a reconstitution study

The LamB protein purified in a solution of sodium dodecyl sulfate was assembled into an ordered hexagonal lattice structure with a lattice constant of about 7.8 nm in the presence of lipopolysaccharide. The LamB alone formed aggregates with some lattice structure. However, the regularity of the lattice was only maintained within a very small area. An ordered hexagonal lattice was also formed when the wild-type lipopolysaccharide was replaced by heptoseless lipopolysaccharide, lipid A, and even fatty acid. However, the lattice constants were appreciably smaller than that with the wild-type lipopolysaccharide. The results suggest that the heptose-containing polysaccharide region, as well as the fatty acid region, are involved in the interaction with the LamB protein. The LamB-lipopolysaccharide lattice was preferably formed on the peptidoglycan layer when the lipoprotein was covalently bound to this layer. These results indicate that the molecular arrangement of the LamB protein in the outer membrane is similar to that of matrix proteins, OmpC and OmpF, which exist as trimers. The ordered hexagonal lattice was active in the receptor function for lambda, resulting in phage adsorption and deoxyribonucleic acid ejection. Thus, this reconstitution system should provide a useful means of studying the mechanism of lambda infection.

Characterization of new membrane lipoproteins and their precursors of Escherichia coli

By labeling cells heavily with [3H]glycerol or [3H]-palmitic acid several new species of lipoproteins, in addition to Braun's lipoprotein and a peptidoglycan-associated lipoprotein called PAL, were found in the envelope of Escherichia coli. The new lipoproteins were immunochemically different from both Braun's lipoprotein and PAL. A strain lacking the structural gene for Braun's lipoprotein contained new lipoproteins and PAL. In addition to Braun's lipoprotein and PAL, four new lipoproteins were found to be localized in the outer membrane, while other two species were found in the cytoplasmic membrane. The localization of one species is unknown. We previously reported that, on treatment of cells with globomycin, a precursor of Braun's lipoprotein accumulated in the cell envelope (Hussain, M., Ichihara, S., and Mizushima, S. (1980) J. Biol. Chem. 255, 3707-3712). Similarly, the putative precursors of new lipoproteins and that of PAL accumulated in globomycin-treated cells. These precursors contained glycerol and fatty acid(s) as that of Braun's lipoprotein did. It is suggested that the structures of the "signal" region and the mechanisms of processing of all the lipoproteins of E. coli are similar.

Specialized transducing bacteriophage lambda carrying the structural gene for a major outer membrane matrix protein of Escherichia coli K-12

A specialized transducing phage lambda carrying the structural gene for the OmpF protein, an outer membrane matrix protein, was isolated. The phage carries the 20.5--21-min region of the Escherichia coli K-12 chromosome and carries asnS, ompF, and aspC genes.

Appearance of elongation factor Tu in the outer membrane of sucrose-dependent spectinomycin-resistant mutants of Escherichia coli

When sucrose-dependent spectinomycin-resistant (Sucd-Spcr) mutants of Escherichia coli were grown in the absence of sucrose, a new protein appeared in the membrane fraction insoluble in Triton X-100. The protein had a hydrophobic nature. However, unlike other outer membrane proteins the new protein was extracted with sodium dodecyl sarcosinate. The new protein was found to be identical with elongation factor Tu (EF-Tu), as judged from the electrophoretic mobility in three different gel systems, coprecipitation with the antiserum against EF-Tu, the profiles of peptide fragments produced with three different proteases and analyses of N-terminal and C-terminal amino acids. This membrane EF-Tu accounted for 5-10% of total cell EF-Tu. When spheroplasts were pretreated with trypsin, EF-Tu in the outer membrane disappeared. Incubation of cytosol EF-Tu with the outer membrane did not result in the binding of EF-Tu to the membrane. These results indicate that the appearance of EF-Tu in the outer membrane is not due to artificial binding during membrane preparation. It is suggested that the ribosomal alteration resulted in dislocation of the cytosol protein into the outer membrane.

Deletion mapping and heterogenote analysis of a mutation responsible for osmosis-sensitive growth, spectinomycin resistance, and alteration of cytoplasmic membrane in Escherichia coli

Lambda transducing phages carrying Escherichia coli deoxyribonucleic acid of various lengths from the aroE-rpsL region were lysogenized into the F'3 plasmid and were used for heterogenote analysis of YM101, a sucrose-dependent, spectinomycin-resistant mutant of E. coli. Three characteristics of the mutant strain, resistance to spectinomycin, sucrose dependence of growth, and lack of I-19 protein in the cytoplasmic membrane, were shown to be the result of a mutation in a region designated delta 53-spcl. This region extends over 3.6-kilobase pairs and is located within a cluster of ribosomal genes. The mutation is recessive to the wild-type allele.

Accumulation of glyceride-containing precursor of the outer membrane lipoprotein in the cytoplasmic membrane of Escherichia coli treated with globomycin

The protein accumulated in the cell envelope of Escherichia coli treated with globomycin was identified as the precursor of the outer membrane lipoprotein. The prolipoprotein was almost exclusively localized in the cytoplasmic membrane. The prolipoprotein could be immunoprecipitated with antilipoprotein immunoglobulin and could be chased to the lipoprotein in both in vivo and in vitro. Globomycin inhibited the chase. The prolipoprotein contained glycerol and fatty acid residues, whereas no free sulfhydryl group was detected in it. From these results, it is concluded that the prolipoprotein possesses a glyceride which is covalently bound to the cysteine residue in the peptide as the lipoprotein does and that the removal of signal peptide takes place after the modification. The inhibition of bacterial growth with increasing concentrations of globomycin was accompanied by a gradual increase in the accumulation of the prolipoprotein. Furthermore, growth of the lipoprotein-negative mutant was highly resistant to globomycin. These results strongly indicate that the accumulation of the prolipoprotein in the cytoplasmic membrane causes the death of cells.

Influence of molecular size and osmolarity of sugars and dextrans on the synthesis of outer membrane proteins O-8 and O-9 of Escherichia coli K-12

Supplementation of the growth medium with high concentrations of sugars or low-molecular-weight dextrans results in a drastic change in the ratio of outer membrane proteins O-8 and O-9, due to induction of O-8 synthesis and suppression of O-9 synthesis. Sugars and dextrans of molecular weights greater than 600 to 700 switched the synthesis of O-9 to that of O-8 more effectively than those of lower molecular weight, although the effect was almost the same within each of the two groups irrespective of the differences in molecular weight within the group. Proteins O-8 or O-9, or both, are responsible for the formation of pores that allow the passive diffusion of hydrophilic molecules whose molecular weights are smaller than about 600 (T. Nakae, Biochem. Biophys. Res. Commun. 71:877-884, 1976). The results indicate that substances that cannot pass through the outer membrane switch the synthesis of O-9 to that of O-8 more effectively than those that can penetrate this membrane with the aid of O-8, O-9, or both. It is suggested that the osmotic pressure exerted on the outer membrane plays an important role in the regulation of synthesis of the two proteins.

Interaction of bacteriophage T4 with reconstituted cell envelopes of Escherichia coli K-12

The interaction with bacteriophage T4 of the cell surface of Escherichia coli K-12 reconstituted from outer membrane protein O-8, lipopolysaccharide, and the lipoprotein-bearing peptidoglycan sacculus was studied. The reconstituted cell surface was active as a receptor for the phage, resulting in the contraction of the tail sheath, a morphological change in the base plate which was accompanied by the extension of short tail pins down to the cell surface and the penetration of the needle through the cell surface. However, the ejection of phage deoxyribonucleic acid did not take place. Both O-8 and lipopolysaccharide were essential for the interaction. In the reconstitution, the wild-type lipopolysaccharide could not be replaced by either heptoseless lipopolysaccharide or lipid A. The lipoprotein-bearing peptidoglycan sacculus was also found to be an active component for the phage adsorption. The sacculus most likely functioned as a basal framework on which O-8 and lipopolysaccharide assembled to form a flat sheet which is large enough to interact with individual distal ends of long tail fibers of a single phage particle.

Arrangement of proteins O-8 and O-9 in outer membrane of Escherichia coli K-12. Existence of homotrimers and heterotrimers

1. The molecular arrangement of major outer membrane proteins O-8 and O-9 that exist as trimers has been studied by means of cross-linking with dimethylsuberimidate. 2. The cross-linked samples were examined on a urea/sodium dodecyl sulfate/polyacrylamide gel which was developed to separate cross-linked trimer and dimer of O-8 from those of O-9. 3. Cells simultaneously synthesizing both O-8 and O-9 formed heterotrimers (trimers containing both proteins) as well as homotrimers. 4. Quantitative analyses revealed that there was no discrimination between O-8 and O-9 in the assembly process to form trimers. 5. When cells were grown sequentially under two different sets of conditions so that the cells synthesized either one of the two proteins in the first stage and the other in the second stage of growth, no heterotrimers were formed. This result indicates that subunit exchange did not take place between trimers which had been incorporated into the outer membrane.

Genetic analysis of a mutation affecting ribosomal protein S1 in Escherichia coli

Ribosomal protein S1 from a newly isolated Escherichia coli mutant has a molecular weight of about 54,000 which is smaller than the wild type S1 (M.W. 65,000). The isoelectric points of the smaller and the wild type S1 species are similar in the gel electrophoresis system of O'Farrell (1975). Genetic analyses by Hfr conjugation and P1 phage transduction indicate that the mutation affecting S1 (rpsA) is located close to the serC gene [20 min on the E. coli genetic map of Bachmann et al. (1976)], with a co-transduction frequency of 61%. The most probable gene order is serC-rpsA-cmlB.

Characterization of a mutant form of ribosomal protein S1 from Escherichia coli

An altered form of ribosomal protein S1 from a mutant of Escherichia coli has been isolated and characterized. The mutant protein (denoted m1-S1) has a molecular weight of 57,000 as shown by sodium dodecyl sulfate-gel electrophoresis and the same NH2-terminal sequence as wild type S1. Protein m1-S1 binds poly(U) in the same manner as protein S1 and is active in protein synthesis with either synthetic or natural mRNA. Thus, about 75% of the sequence of protein S1 (which includes the NH2-terminal region) contains essentially all the functional domains of this protein involved in protein biosynthesis.

Role of lipopolysaccharide and outer membrane protein of Escherichia coli K-12 in the receptor activity for bacteriophage T4

Lipopolysaccharide isolated from Escherichia coli K-12 did not inactivate phage T4, although the cell envelopes with 1% sodium deoxycholate resulted in the release of cytoplasmic membrane proteins, 70% of the lipopolysaccharide, and almost all of the phospholipid. The reconstitution of phage receptor activity was achieved from deoxycholate-soluble and -insoluble fractions by dialysis against a solution of magnesium chloride. Lipopolysaccharide was the only essential component in the deoxycholate-soluble fraction. PhageT4-resistant mutants YA21-6 and YA21-82, having defects in the deoxycholate-soluble and -insoluble fractions, respectively, were isolated. The deoxycholate-soluble fraction of YA21-6 possessed heptoseless lipopolysaccharide, and this defect was responsible for the phage resistance. The deoxycholate-insoluble fraction of YA21-82 lacked outer membrane protein O-8. The addition of O-8 to this fraction together with the wild-type lipopolysaccharide resulted in the appearance of the receptor activity. Furthermore, the reconstitution was successfully achieved with only O-8 and the wild-type lipopolysaccharide, indicating that O-8 was an essential component in the deoxycholate-insoluble fraction.

Reconstitution of an ordered structure from major outer membrane constituents and the lipoprotein-bearing peptidoglycan sacculus of Escherichia coli

An ordered hexagonal lattice structure with a lattice constant of about 7 nm was reconstituted on the entire surface of the lipoprotein-bearing peptidoglycan from outer membrane protein O-8 and lipopolysaccharide. The lattice structure resembled that observed in the cell envelope which had been treated with sodium dodecyl sulfate (Steven et al., J. Cell Biol. 72:292-301, 1977). The omission of either O-8 or lipopolysaccharide resulted in the failure of formation of the lattice structure. No ordered lattice was formed on the peptidoglycan lacking the bound form of the lipoprotein. In the absence of the lipoprotein-bearing peptidoglycan, O-8 and lipopolysaccharide assembled into vesicles with an ordered hexagonal lattice, the lattice constant of which was also about 7 nm. A preliminary experiment indicated that protein O-9 gave the same result as did O-8. These results strongly indicate that O-8 and/or O-9 and lipopolysaccharide provide the ordered framework of the outer membrane and that the bound form of the lipoprotein plays a role in the holding of the framework on the peptidoglycan layer.

Removal by bovine serum albumin of fatty acids from membrane vesicles and its effect on proline transport activity in Escherichia coli

Bovine serum albumin appreciably stimulated the initial rate and the steady-state level of proline uptake in membrane vesicles, while it had no effect on the oxidase activity for ascorbate-phenazine methosulfate, on which the transport activity depends. Bovine serum albumin showed the strongest stimulatory effect on the transport system among the proteins tested. Three other proteins did not show any effect, while beta-lactoglobulin showed a weaker but appreciable effect on the transport activity. The incubation of membrane vesicles with bovine serum albumin resulted in extensive removal of fatty acids, while none of the other membrane components, including proteins and phospholipids, was removed by this treatment. Fatty acids inhibited the proline transport activity, while the inhibited activity was appreciably restored by incubation with the albumin. An experiment with radioactive fatty acids showed that exogenously-added fatty acids bound firmly to the membrane vesicles and were removed by subsequent incubation with the albumin. The incubation of membrane vesicles for several hours resulted in an increase of fatty acids with a concomitant loss of the transport activity. Subsequent incubation with the albumin resulted in the removal of fatty acids and the partial restoration of the transport activity. Based on these results, it is concluded that bovine serum albumin specifically removed fatty acids from membrane vesicles, resulting in activation of the proline transport system.

Characterization of major outer membrane proteins O-8 and O-9 of Escherichia coli K-12. Evidence that structural genes for the two proteins are different

Outer membrane proteins O-8 and O-9 have been highly purified from a strain of Escherichia coli K-12 by Sephadex G-200 and DEAE-cellulose chromatographies. The amino acid compositions of the purified proteins were definitely different, although they showed marked similarities. The profiles of BrCN peptides of the two proteins were also different. None of the BrCN peptides were the same for the two proteins. Analysis of the first twelve N-terminal residues revealed that the two proteins are strikingly similar, but with differences in the third and the eleventh amino acid residues. It can be concluded that proteins O-8 and O-9 are products of different structural genes which developed by duplication of an ancestral genome followed by mutation.

Identification of an outer membrane protein responsible for the binding of the Fe-enterochelin complex to Escherichia coli cells

Escherichia coli incorporates iron as a complex with enterochelin. By using mutants which lack one or the other, or both, of the outer membrane proteins, O-2b and O-3, we have shown that protein O-2b (feuB protein) is responsible for the primary binding of the iron-enterochelin complex to the outer membrane in the process of iron transport.

Interaction of the cytoplasmic membrane and ribosomes in Escherichia coli; altered ribosomal proteins in sucrose-dependent spectinomycin-resistant mutants

Alterations in the ribosomes of sucrose-dependent spectinomycin-resistant (Sucd-Spcr) mutants of Escherichia coli were studied. Subunit exchange experiments showed that 30S subunits were responsible for the resistance of ribosomes to spectinomycin in all Sucd-Spcr mutants tested. Proteins of 30S ribosomes were analyzed by carboxymethyl cellulose column chromatography based on their elution positions. Mutants YM22 and YM93 had an altered 30S ribosomal protein component, S5, and mutant YM50 had an altered protein, S4. Although a shift of elution position was not detected for all the 30S ribosomal proteins from mutant YM101, the amount of protein S3 was appreciably lowered in the isolated 30S subunits. A partial reconstitution experiment with protein S3 prepared from both the wild-type strain and YM101 revealed that the mutant had altered protein S3 which is responsible for the spectinomycin resistance. These alterations in 30S subunits are discussed in relation to the interaction between ribosomes and the cytoplasmic membrane.