Search PubMed⌕ Search

Biomedical subjects

F G Hansen

Publications and source records attributed to F G Hansen.

54 records · Page 3Linked to original sources
PubMed1983

Effect of dnaA and rpoB mutations on attenuation in the trp operon of Escherichia coli.

The rate of synthesis of tryptophan synthetase was found to be increased by heat inactivation of the dnaA protein in three dnaA mutants temperature sensitive for initiation of DNA replication. The effect of the dnaA mutations was dependent upon the presence of an intact attenuator in the tryptophan operon. The activity of the mutated dnaA protein at the tryptophan attenuator and its activity as initiator for chromosome replication decreased gradually with increasing temperature. Two rpoB mutations that suppress the temperature defect of the dnaA46 mutation in initiation of replication were tested for effects on attenuation in the tryptophan operon. One of the rpoB mutations caused increased transcription termination at the attenuator independent of the dnaA allele, whereas the other mutation had no effect. Expression of the histidine and threonine operons, which are also regulated by attenuation, was unaffected by the dnaA mutations.

Bacterial Proteins↗
PubMed1982

The nucleotide sequence of the dnaA gene and the first part of the dnaN gene of Escherichia coli K-12.

The nucleotide sequence of the dnaA gene and the first 10% of the dnaN gene was determined. From the nucleotide sequence the amino acid sequence of the dnaA gene product was derived. It is a basic protein of 467 amino acid residues with a molecular weight of 52.5 kD. The expression of the dnaA gene is in the counterclockwise direction like the one of the dnaN gene, for which potential startsites were found.

Amino Acid Sequence↗
PubMed1982

The nucleotide sequence of the dnaA gene promoter and of the adjacent rpmH gene, coding for the ribosomal protein L34, of Escherichia coli.

The nucleotide sequence was determined of a 945-bp EcoRI fragment from the Escherichia coli K-12 chromosome at 82 min containing the promoter region of the dnaA gene. This nucleotide sequence contained a coding sequence identical to the amino acid sequence of the ribosomal protein L34 , designated rpmH . The rimA mutation, which affects the maturation of 50S ribosomal particles, may be an allele of the rpmH gene since it maps close to, or within, the L34 coding sequence. The rpmH gene and the dnaA gene are transcribed in the clockwise and counter-clockwise direction, respectively. Nuclease S1 mapping of transcripts indicated the existence of two major promoters for the L34 gene and two promoters for the dnaA gene within the 945-bp EcoRI fragment.

Alleles↗
PubMed1982

The membrane bound ATP synthase of Escherichia coli: a review of structural and functional analyses of the atp operon.

The structure of the atp operon, which contains the genes for the eight subunits alpha, beta, gamma, delta, epsilon, a, b and c of the membrane bound ATP synthase of Escherichia coli as determined by genetic experiments and DNA sequencing, is reviewed. The localization of transcription signals, namely of one major and two minor promoters, as well as the determination of the stoichiometry of the subunits (alpha:beta:gamma:delta:epsilon:a:b:c = 3:3:1:1:1:1:2:12-15) is summarized.

ATP Synthetase Complexes↗
PubMed1981

The genes for the eight subunits of the membrane bound ATP synthase of Escherichia coli.

The genes for the eight subunits of the membrane bound ATP synthase of Escherichia coli (Ca++, Mg++ dependent ATPase, EC 3.6.1.3) were mapped through genetic, physical and functional analysis of specialized transducing phages lambda asn (von Meyenburg et al. 1978). The ATP synthase genes, designated atp1, are located at 83.2 min in a segment of the chromosome between 3.5 and 11.3 kb left (counterclockwise) of the origin of replication oriC. The counterclockwise order of the genes for the eight subunits, the expression of which starts from a control region at 3.5 kb-L, was found to be: a, (c, b, delta), alpha, gamma, (epsilon, beta) which in the notation of Downie el al. (1981) reads atp B (EFH) A G (C D). The analysis was in part based on the isolation of new types of atp (unc, Suc-) mutations. We made use of the fact that specialized transducing phages lambda asn carrying oriC can establish themselves as minichromosomes rendering asnA cells Asn+, and that the resulting Asn+ cells grow slowly if the lambda asn carries part or all of the atp operon. Selecting for fast growing strains mutations were isolated on the lambda asn which either eliminated atp genes or affected their expression ("promoter" mutations). The relationship between these atp mutations and the cop mutations of Ogura et al. (1980), which also appear to map in front of or within the atp genes, is discussed.

Bacteriophage lambda↗
PubMed1981

The nucleotide sequence of the atp genes coding for the F0 subunits a, b, c and the F1 subunit delta of the membrane bound ATP synthase of Escherichia coli.

The nucleotide sequence has been determined of a 2,500 base pair segment of the E. coli chromosome located between 3.75 and 6.25 kb counterclockwise of the origin of replication at 83.5 min. The sequence contains the atp genes coding for subunits a-, b-, c-, delta- and part of the alpha-subunit of the membrane bound ATP synthase. The precise start positions of the atpE (c), atpF (b), atpH (delta) and atpA (alpha) genes have been defined by comparison of the potential coding sequences with the known amino acid sequence of the c-subunit and the determined N-terminal amino acid sequences of the respective subunits. The genes are expressed in the counterclockwise direction. Their order (counterclockwise) is: atpB (a), atpE (c), atpF (b), atpH (delta) and atpA(alpha). The coding sequences for subunits b and delta yield polypeptides of 156 and 177 amino acids, respectively, in accordance with the established sizes of these subunits; the one for the c-subunit, the DCCD binding protein, fits perfectly with its known sequence of 79 amino acids. The a-subunit is comprised within a coding sequence yielding a polypeptide of 271 amino acids. It is suggested, however, that the a-subunit (atpB) contains only 201 amino acids, in accordance with its known size, starting from a translation initiation site within the larger coding sequence. The stoichiometry of the F0 sector subunits is discussed and a model is proposed for the functioning of the highly charged b-subunit of the F0 sector as the actual proton conductor.

ATP Synthetase Complexes↗
PubMed1981

The nucleotide sequence of the replication control region of the resistance plasmid R1drd-19.

The region of plasmid R 1 containing the replication control genes has been sequenced using the Maxam-Gilbert method. The nucleotide sequence of two small PstI restriction fragments (a total of about 1,000 base pairs) was determined for the wild-type R 1 plasmid as well as for two different copy mutants. It was found that one copy mutant has a single base substitution in the fragment which was recently shown to harbor an important inc/cop gene (Molin and Nordström 1980). Furthermore, the sequence indicates the presence of a structural gene that codes for a polypeptide of size 10,500 daltons. Possible gene products predicted from the nucleotide sequences and their role in replication control are discussed.

Base Sequence↗
PubMed1980

Genetic and physical mapping of recF in Escherichia coli K-12.

Two factor transductional crosses place recF at approximately 82 min on the E. coli chromosome; recF is highly cotransducible with dnaA and gyrB (cou). Transductional analysis with a series of lambda tna specialized transducing phages carrying chromosomal DNA from the tnaA region place recF between dnaA and gyrB. This analysis also indicates that a gene lying in the same region and producing an easily detectable protein (estimated MW of 45 kD) is dnaN and not recF.

Bacteriophage lambda↗
PubMed1979

Characterization of the dnaA, gyrB and other genes in the dnaA region of the Escherichia coli chromosome on specialized transducing phages lambda tna.

Specialized transducing phages lambda tna (tryptophanase) harboring chromosomal DNA and genetic markers from the dnaA region of the Escherichia coli chromosome were isolated. Transductional analysis showed that some of these tnaA transducing phages carry two genes important in DNA replication, namely the dnaA gene (initiation of chromosome replication) and the gyrB gene (subunit B of DNA gyrase), formerly designated couR. The following clockwise order of genetic markers was found: uhp, gyrB, dnaA, rimA, tnaA, bglB. The gene-protein relationship was established by the determination of the gene products encoded on the chromosomal DNA of the different lambda tna. A 54 kD and a 91 kD polypeptide appear to be coded for by the dnaA and gyrB genes, respectively; the 91 kD protein is encoded on a region in which coumermycin sensitivity maps and is with respect to electrophoretic behavior identical to subunit B of DNA gyrase. The 54 kD protein is encoded on the region in which different independently isolated dnaA(Ts) mutations (dnaA5, dnaA46, dnaA167, dnaA203, dnaA204, dnaA205, dnaA211, dnaA508) are located. Additional genes which code for polypeptides with hitherto unknown functions were identified and mapped. The acriflavin sensitivity mutation acrB1 was found to be an allele of the gyrB gene (see "Note Added in Proof").

Bacteriophage lambda↗
PubMed1979

Nucleotide sequence of the origin of replication of the Escherichia coli K-12 chromosome.

The origin of replication, oriC, of the Escherichia coli chromosome was mapped within a DNA segment of 422 base pairs. The nucleotide sequence of this segment was determined. The source of DNA for the sequence analysis was a minichromosome constructed in vivo, consisting exclusively of chromosomal DNA and a minichromosome constructed by cloning in vitro. The nucleotide sequence of the replication origin is characterized by a high degree of repetitiveness due to both inverted and direct repeats. Sequence homologies were found between portions of the replication origins of E. coli and phages lambda and G4. This suggests similarities in some steps in the initiation of replication of the different replicons.

Base Sequence↗
PubMed1978

Mini-chromosomes: plasmids which carry the E. coli replication origin.

We have isolated plasmids by linking the 5.9 MD EcoRI fragment of E. coli that carries the origin of replication to an EcoRI fragment that carries an amplicillin resistance determinant, but lacks an origin of replication. 3 plasmids of this type, pOC1, pOC2, and pOC3, are described in detail in this report. Although the plasmids have some adverse effect on the growth properties of the host strain, their existence shows that two functioning chromosomal origins can coexist in one cell. Deletions generated from this type of plasmids allow an allocation of the origin of replication of E. coli within a DNA segment less than 0.4 MD in size.

Ampicillin↗
PubMed1978

Origin of replication, oriC, or the Escherichia coli chromosome on specialized transducing phages lambda asn.

Specialized transducing phages lambda asn harboring chromosomal DNA and genetic markers on either side of the asn gene were isolated. Phages carrying chromosomal DNA counterclockwise of the asn gene can upon infection establish themselves as self-replicating plasmids in asn, recA hosts lysogenic for lambda. It is concluded that this bypassing of normal lambda immunity is due to the presence of the chromosomal replication origin, oriC, in this class of phages. Genetic analysis and the determination of restriction endonuclease cleavage patterns of the different lambda asn lead to the allocation of oriC within 1.5 megadaltons of the asn gene towards the uncA, uncB genes at 82 min on the genetic map of E. coli. The clockwise order of genes on the chromosomes is found to be: bglB, (pst, glmS), (uncA, uncB), oriC, asn, trkD, rbs, rrnC, ilv.

Chromosome Mapping↗
PubMed1977

Origin of replication, oriC, of the Escherichia coli chromosome: mapping of genes relative to R.EcoRI cleavage sites in the oriC region.

A precise genetic-physical map of the tna-ilv region at 82 min on the genetic map of E. coli is obtained through deletion mapping and analysis by restriction endonuclease EcoRI of plasmids, derived from an F' carrying the genes between aroE and ilv. A locus, designated het, which in its diploid state results in slow growth and heterogeneity of cell size due to distorted cell division, maps between bglB and asn, 30-45 kb counterclockwise of ilv. The pattern of R.EcoRI cleavage sites in the het region is identical with the pattern obtained by Marsh and Worcel (1977) who analyzed DNA labeled preferentially in the region of the DNA replication origin (oriC). We suggest that oriC is identical with the het site and that it can be allocated to a position 32 kb counterclockwise of the ilv operon.

Chromosome Mapping↗
PubMed1977

Regulation of the dnaA product in Escherichia coli.

When an E. coli mutant (CRT46, dnaA46), thermosensitive in the initiation of DNA replication, grows at intermediate temperatures its DNA/mass ratio is somewhat lower than normal, but the cells possess an excess of initiation capacity, which can be expressed in the absence of protein synthesis and lead to the accumulation of anomalously high amounts of DNA. A shift-up in temperature causes inhibition of initiation, and at the same time the production of initiation capacity is accelerated. After a shift-down in temperature initiation is released but the production of capacity is inhibited. The initiation capacity is thermolabile. The simplest explanation of these observations is that the dnaA product has a dual role: a positive function as an initiator of replication and a negative control function in its own synthesis.

DNA Replication↗
PubMedDate not supplied

The initiator titration model: computer simulation of chromosome and minichromosome control.

The initiator titration model was formulated to explain the initiation control of the bacterial chromosome. In particular, features concerning the replication behaviour of minichromosomes, such as their high copy number and Escherichia coli's ability to coinitiate chromosome and many minichromosome origins, were considered during the formulation of the model. The model is based on the initiator protein DnaA and its binding sites, DnaA boxes, in oriC, in the dnaA promoter and at other positions on the chromosome. Another important factor in the model is the eclipse period created by the hemimethylation of a new oriC which makes it refractory to initiation. The model was analysed by computer simulations using a stochastic approach varying the different input parameters, and the resulting computer cells were compared with data on living E. coli cells. Here we present the outcome of a few of these simulations concerning the eclipse period, in silico-shift experiments blocking initiation or elongation of replication, and introduction of minichromosomes into the computer cells. We also discuss the synthesis of DnaA protein in the computer cells. From our simulations, we conclude that, whether true or not, the model can mimic the in vivo initiation control of E. coli.

Bacterial Proteins↗