Biomedical subjects

S J Projan

Publications and source records attributed to S J Projan.

60 records · Page 4Linked to original sources

PubMed1983

Determination of plasmid copy number by fluorescence densitometry.

A simple and reliable method for the determination of plasmid copy numbers by direct fluorescence densitometry of ethidium bromide-stained electrophoretic gels was developed. In developing the method, the following parameters were evaluated and controlled: plasmid DNA trapping in the linear chromosomal DNA, staining-destaining kinetics for ethidium bromide, linearity of the fluorescence response, and the effect of the molecular topology of DNA on ethidium bromide binding to DNA in agarose.

DNA, Bacterial↗

PubMed1981

Initiation of chromosomal DNA synthesis in vitro.

An in vitro complementation assay for initiation of chromosomal DNA replication is described. The initiation reaction is dependent upon extract from either of two hybrid-plasmid containing strains. Each hybrid plasmid carries a suppressor of dna A-ts mutations. The in vitro DNA synthesis is heavily biased toward the origin region, and the origin of replication (oriC) is replicated as determined by DNA-DNA hybridizations.

Chromosomes, Bacterial↗

PubMed1981

Complementation of a dnaC initiation defect in vitro.

The dnaC28 mutant, CT28-3b, is an initiation defective dnaC strain. Extracts of the mutant failed to synthesize DNA in vitro when the strain was incubated at the restrictive temperature for two generation times prior to preparation of the extract. Addition of a complementing extract from a Col-E1::dnaC+ hybrid plasmid containing strain or of partially purified dnaC protein resulted in substantial synthesis. Hybridization of the DNA made by these in vitro complementation extracts showed that a significant portion of this DNA was from the region near the chromosomal origin of replication.

Bacteriophage lambda↗

PubMed1981

RNA polymerase is required for DNA initiation in vitro.

We have previously reported in vitro complementation assays for chromosome initiation that enable dnaA and dnaC mutant extracts to synthesize DNA. To examine the role of RNA polymerase in chromosome initiation, inhibitors of the enzyme and anti-RNA polymerase antibody were used. Though rifampicin failed to efficiently inhibit ribonucleoside triphosphate polymerization under the assay conditions, both streptolydigin and anti-RNA polymerase antibody abolished ribonucleic acid synthesis completely. Antibody effectively inhibited chromosome initiation in the dnaA mutant based reaction but streptolydigin did not. Neither streptolydigin nor antibody affected the dnaC-dependent assay. It was concluded that RNA polymerase is required for initiation but not necessarily to polymerize a polyribonucleotide. A scheme for the sequence of initiation events is presented.

Aminoglycosides↗

PubMed1981

Isolation and analysis of multicopy extragenic suppressors of dnaA mutations.

Recombinant plasmids were constructed from restriction enzyme digests of Escherichia coli chromosomal deoxyribonucleic acid and pMB9 plasmid deoxyribonucleic acid and selected for correction of the dnaA phenotype. The three plasmids isolated, all retransformed dnaA cells, both recA+ and recA, such that all tetracycline-resistant transformants selected at permissive temperature simultaneously became temperature resistant. Restriction enzyme mapping of the plasmids showed all three to be different, and it was subsequently shown that none contained the dnaA+ gene. Though each of the three plasmids suppressed three different temperature-sensitive dnaA alleles, none corrected the phenotype of an unsuppressed dnaA amber allele. It was concluded, therefore, that each plasmid contained a unique extragenic suppressor of dnaA and that the suppression was observed because of the elevated gene dosage of the cloned material. The plasmids were unstable in the absence of selection.

DNA Replication↗

PubMedDate not supplied

Toxic shock syndrome toxin 1 is encoded by a variable genetic element.

The primary cause of toxic shock syndrome is toxic shock syndrome toxin 1 (TSST-1), a 22,049-dalton exotoxin. Approximately 20% of Staphylococcus aureus isolates produce TSST-1; the production of this toxin is therefore a variable genetic trait. The TSST-1 gene and its flanking sequences are found on a genetic element that is present in TSST-1-positive isolates and absent in TSST-1-negative isolates. Preliminary sequence data and Southern hybridization experiments with the cloned flanking sequences have provided evidence that the TSST-1 element is 4-7 kilobases in size. Hybridization analysis of whole-cell DNA from two genetically mapped TSST-1-positive strains has demonstrated that the TSST-1 element has at least two chromosomal locations. This finding suggests that the element is mobile. Biotyping of 75 TSST-1-positive isolates showed that the large majority were tryptophan-negative, and Southern hybridization analysis of whole-cell DNA from these isolates revealed a common blotting pattern--an observation suggesting that these strains are clonal.

Animals↗