We have developed a cell-free system from Escherichia coli for studying illegitimate recombination between nonhomologous DNA molecules. The recombination is stimulated by oxolinic acid, an inhibitor of DNA gyrase. The stimulation is abolished by coumermycin A1 and is not found in extracts of nalidixic acid-resistant (gyrA) mutants. We therefore inferred that DNA gyrase directly participates in ...

Real-time QPCR based methods for determination of plasmid copy number in recombinant Escherichia coli cultures are presented. Two compatible methods based on absolute and relative analyses were tested with recombinant E. coli DH5alpha harboring pBR322, which is a common bacterial cloning vector. The separate detection of the plasmid and the host chromosomal DNA was achieved using two separate p...

We have attempted to introduce some eukaryotic and prokaryotic DNA sequences into mouse fibroblasts. Purified herpes thymidine kinase gene (tk) was introduced into mouse cells. The presence of the herpes tk gene was established by gel electrophoresis, sensitivity to the purine analog acyloguanosine, and Southern blot hybridization. We utilized two different methods to introduce nonselectable ma...

While humans use antibiotics at inhibitory levels to prevent microbial growth, antibiotics are normally found at sub-inhibitory concentrations in nature. The role and effects of sub-inhibitory levels of antibiotics is one of the key areas of research in microbial science today. In this experiment, the effects of sub-inhibitory levels of chloramphenicol on pBR322 plasmid copy number in Escherich...

Escherichia coli chromosome DNA was observed previously to consist of subunits of Archimedean spirallike supercoiling. How do cells build such a DNA structure remains unknown. In the present study, atomic force microscopy (AFM) images showed that supercoiled pBR322 DNA forms a spiral structure upon intercalation with 0.5 μg/ml ethidium bromide (EB), which used to be considered as zero superheli...

rnh (formerly termed sdrA) mutants of Escherichia coli K-12, capable of continuous DNA replication in the absence of protein synthesis (stable DNA replication), are devoid of ribonuclease H (RNase H, EC 3.1.26.4) activity. Plasmid pBR322 was found to replicate in rnh mutants in the absence of DNA polymerase I, the polA gene product, which is normally required for replication of this plasmid. Th...

objective: dna markers are one of the most important indicators for estimating molecular weight of dna samples, although it used in widespread medical and research laboratories. these markers are very divers and have been prepared in different manners and from different sources of dna. but unfortunately, dna markers haven't been made in our country and all of the markers that we use are made in...