Biomedical subjects

T Atlung

Publications and source records attributed to T Atlung.

43 records · Page 3Linked to original sources

PubMed1984

Allele-specific suppression of dnaA(Ts) mutations by rpoB mutations in Escherichia coli.

Extragenic suppressor mutations for dnaA (Ts) mutations mapping in the rpoB gene (beta-subunit of RNA polymerase) were isolated by selection of spontaneous rifampicin resistant mutants and screening for temperature resistance. Six rpoB mutations were analysed for suppression of 12 different dnaA (Ts) mutations. The analysis showed that all dnaA(Ts) mutations could be suppressed by some rpoB mutation. All six rpoB mutations showed allele specificity when tested for suppression of 12 dnaA(Ts) mutant strains. The allele specificity was found to correlate with the map position of the dnaA (Ts) alleles.

Alleles↗

PubMed1984

dnaA suppressor (dasF) mutants of Escherichia coli are stable DNA replication (sdrA/rnh) mutants.

The possible allelic relationship between dasF (dnaA suppressor) and sdrA/rnh (stable DNA replication/RNase H) mutations was examined. dasF mutations could not only suppress various dnaA(ts) mutations, but also the insertional inactivation of the dnaA gene or deletion of the oriC sequence, as could sdrA mutations. dasF mutants were found to exhibit the stable DNA replication phenotype, and the sensitivity to rich media, of sdrA mutants. The dasF and sdrA mutations were mapped very closely between metD and proA on the E. coli genetic map. The mutations were recessive to the wild-type allele for all the above phenotypes. It was concluded that dasF is allelic to sdrA/mh.

Alleles↗

PubMed1984

Fine structure genetic map and complementation analysis of mutations in the dnaA gene of Escherichia coli.

A fine structure genetic map of several mutations in the dnaA gene of Escherichia coli was constructed by the use of recombinant lambda and M13 phages. The dnaA508 mutation was found to be the mutation most proximal to the promoter, while the dnaA203 mutation was found to be the most distal one. The order of mutations established in this analysis was: dnaA508, dnaA167, (dnaA5, dnaA46, dnaA211), dnaA205, dnaA204, dnaA203. The mutations dnaA601, dnaA602, dnaA603, dnaA604 and dnaA606 were found to map very close to each other and close to dnaA205 in the middle third of the dnaA gene. In analysing the dominance relationship all 13 dnaA mutations were found to be recessive to the wild type. Characteristic phenotypes of the dnaA(Ts) mutants, like reversibility of the temperature inactivation of the dnaA protein, cold sensitivity of haploid or of merodiploid strains and suppressibility by rpoB mutations, are found to correlate with clusters of mutations within the gene.

Bacterial Proteins↗

PubMed1983

Conditional change of DNA replication control in an RNA polymerase mutant of Escherichia coli.

A temperature-sensitive mutant of Escherichia coli with a temperature-dependent change in the control of initiation of DNA replication was isolated. The phenotype of the mutant was dependent on a mutation in the RNA polymerase gene rpoC. In vitro RNA polymerase activity was temperature sensitive. The mutant grew and synthesized DNA at 30 degrees C as did the wild type. After a shift to 39 degrees C, a temperature still permissive for growth, the mutant increased its origin concentration more than twofold. After a shift from 39 to 30 degrees C, initiation of DNA replication was inhibited until the normal origin concentration was reestablished.

DNA Replication↗

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 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↗

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↗