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Biomedical subjects

M Schaechter

Publications and source records attributed to M Schaechter.

At least 19 recordsLinked to original sources
PubMed2001

Escherichia coli and Salmonella 2000: the view from here.

Five years after the publication of the second edition of the reference book Escherichia coli and Salmonella: Cellular and Molecular Biology, and on the eve of launching a successor venture, the editors and colleagues examine where we stand in our quest for an understanding of these organisms. The main areas selected for this brief inquiry are genomics, evolution, molecular multifunctionality, functional backups, regulation of gene expression, cell biology, sensing of the environment, and ecology.

Biological Evolution↗
PubMed1999

A paean to Microbiology and Molecular Biology Reviews.

This article celebrates the accomplishments of Microbiology and Molecular Biology Reviews from its early days to the present time. The importance of this journal in the professional lives of microbiologists is emphasized, and examples of outstanding reviews are presented.

History, 20th Century↗
PubMed1994

SeqA limits DnaA activity in replication from oriC in Escherichia coli.

A mutant Escherichia coli that transforms minichromosomes with high efficiency in the absence of Dam methylation has been isolated and the mutation mapped to 16.25 min on the E. coli map. The mutant strain containing seqA2 is defective for growth in rich medium but not in minimal medium. A similar mutation in this gene, named seqA1, has also been isolated. Here we show that the product of the seqA gene, SeqA, normally acts as an inhibitor of chromosomal initiation. In the seqA2-containing mutant, the frequency of initiation increases by a factor of three. Introduction of the wild-type seqA gene on a low-copy plasmid suppresses the cold sensitivity of a dnaAcos mutant known to overinitiate at temperatures below 39 degrees C. In addition, the seqA2 mutation is a suppressor of several dnaA (Ts) alleles. The seqA2 mutant overinitiates replication from oriC and displays the asynchronous initiation phenotype. Also the seqA2 mutant has an elevated level of DnaA protein (twofold). The introduction of minichromosomes or a low-copy-number plasmid carrying five DnaA-boxes from the oriC region increases the growth rate of the seqA2 mutant in rich medium to the wild-type level, reduces overinitiation but does not restore synchrony. We propose that the role of SeqA is to limit the activity level of the E. coli regulator of chromosome initiation, DnaA.

Bacterial Outer Membrane Proteins↗
PubMed1993

Teaching microbiology to medical students.

Medical education is undergoing radical changes. The author discusses his views regarding the issues of content, process, and evaluation of teaching microbiology to medical students.

Education, Medical, Undergraduate↗
PubMed1989

In vivo studies of DnaA binding to the origin of replication of Escherichia coli.

We have shown that DnaA, a protein required for initiation of DNA replication in Escherichia coli, binds to three of four DnaA binding sequences in the replicative origin oriC (boxes R1, R2 and R4). Protein-oriC DNA interactions in minichromosomes carried by wild-type and dnaA mutant strains were demonstrated by in vivo footprinting using dimethylsulfate treatment of intact cells. The same characteristic enhancement/protection pattern was seen in wild-type minichromosomes or mutants defective in oriC function but carrying the four DnaA boxes. Minichromosomes in dnaA (Ts) mutants showed no protein binding at non-permissive temperatures and reduced binding even at permissive temperatures. In vivo footprints of the wild-type strain were identical to those obtained in vitro using purified DnaA proteins and oriC DNA. Transcription into oriC affected the binding of DnaA protein to the DnaA boxes. These findings suggest that the protein causing the in vivo footprints at oriC is DnaA.

Bacterial Proteins↗
PubMed1988

The replicative origin of the E. coli chromosome binds to cell membranes only when hemimethylated.

DNA from the E. coli replicative origin binds with high affinity to outer membrane preparations. Specific binding regions are contained within a 463 bp stretch of origin DNA between positions -46 and +417 on the oriC map. This region of DNA contains an unusually high number of GATC sites, the recognition sequence for the E. coli DNA adenine methylase. We show here that oriC DNA binds to membrane only when it is hemimethylated. The E. coli chromosomal origin is hemimethylated for 8-10 min after initiation of replication, and origin DNA binds to membranes only during this time period. Based on these results, we propose a speculative model for chromosome segregation in E. coli.

Cell Membrane↗
PubMed1984

Direct evidence for specific binding of the replicative origin of the Escherichia coli chromosome to the membrane.

The origin of replication of the Escherichia coli chromosomal DNA binds with high affinity to outer membrane preparations. This specific binding requires a 463-base-pair region of origin DNA between positions -45 and +417 of the oriC map. We show that binding does not require the presence of adjacent regions. From further analysis, we conclude that more than one binding site resides within the 325-base-pair fragment between positions +38 (BamHI) and +417 (XhoI). When this fragment is cut, two pieces bind with high affinity and one binds with lesser affinity. The binding ability of one of the high affinity sites is abolished by cutting it at position +92 with BamHI.

Binding Sites↗
PubMed1982

Binding of the origin of replication of Escherichia coli to the outer membrane.

The replication origin of the Escherichia coli chromosome binds with high affinity to outer membrane preparations. This binding requires a 460 bp stretch of origin DNA between positions -40 and 420 of the oriC map. Specific binding can be detected by the use of a membrane filter retention assay in the presence of excess calf thymus DNA. This binding is enhanced by divalent cations and takes place specifically at a few (0.7-3.0) membrane sites per cell. The apparent affinity of origin DNA for membranes is enhanced by two peptides, (55 kilodaltons (kd) and 75 kd), which remain attached to the DNA through treatment with 5.5 M cesium chloride.

Bacterial Proteins↗
PubMed1980

Isolation of a replication origin complex from Escherichia coli.

A complex consisting of replicative origin DNA and several proteins was isolated from Escherichia coli. Cells of temperature-sensitive mutants were labeled at the origin and fractionated by sucrose gradient centrifugation. A complex highly purified in origin DNA sedimented as a unique band. This complex dissociated at high concentration, above 0.2 M KCl. Upon dialysis, the complex reformed, allowing further purification of its constituents. Three major protein bands were found, corresponding to proteins of the outer membrane. The complex did not sediment with membrane fractions, but adhered to the outer membrane in the presence of magnesium.

Bacterial Proteins↗
PubMed1980

Translocation of phospholipids from the inner to the outer membrane of Escherichia coli.

The translocation of lipids from the inner to the outer membrane of Escherichia coli has been investigated by pulse-chase experiments. After a pulse with [2-3H]glycerol, the specific activity of the newly synthesized [3H]phosphatidylethanolamine was 5 times greater in the inner than in the outer membrane. During the chase, [3H]phosphatidylethanolamine was translocated to the outer membrane. At 37 degrees C, the half-life for translocation was 2.8 min. This rate was not influenced by alteration in the cellular growth rate at 37 degrees C. Altering the cellular growth temperature had a pronounced effect on the rate of phosphatidylethanolamine translocation. Energy inhibitors that deplete the protonmotive force markedly inhibited the translocation. Translocation was not affected by inhibitors of ATP, protein, or lipid synthesis. Phosphatidylglycerol and cardiolipin are transfocated very rapidly, with half-lives shorter than 30 sec.

Bacterial Proteins↗
PubMed1977

Release of Escherichia coli DNA from membrane complexes by single-strand endonucleases.

Treatment of gently prepared lysates of Escherichia coli with single-strand-specific endonuclease (SI or from mung beans) results in the release of about 90% of the DNA from membranes, as determined by the M band technique. The released DNA has an average molecular weight of about 1.2 X 10(8). Data obtained with endonuclease S1 fit a mathematical model in which substrate sites are at or near membrane attachment sites. Data obtained with pancreatic deoxyribonuclease or x-rays fit a model for double-strand breaks at random sites along the DNA. Fitting data to these models, we estimate that there are 18+/-5 membrane attachment sites. The DNA remaining after S1 nuclease treatment is enriched for the region near the origin of chromosome replication. Therefore, attachment at this region near the origin of chromosome replication. Therefore, attachment at this region appears to be chemically different from that at the other sites along the DNA.

Animals↗
PubMed1973

Turnover of phosphatidylglycerol in Escherichia coli.

In growing cultures of Escherichia coli, the nonacylated glycerol of phosphatidylglycerol (PG) is labeled more rapidly than is the acylated glycerol. This is, in part, due to a rapid exchange reaction of the nonacylated glycerol. Only some of the PG molecules undergo this reaction while others are stable. Using a mutant unable to make glycerophosphate, we have shown that the nonacylated glycerol of PG can exchange with non-phosphorylated glycerol.

Acylation↗