Bacteriophages, DNA

Knots nd Ca.tena.nes, Closed-circular DNA hehces can cross over one another three or more times to form topological knots. These stmctures are not common, but have been found to occur naturally in some bacteriophage DNAs. 

In E. coli cells, DNA replication starts at a specific site called oriC. The oriC locus contains only 245 base pairs. Similar sequences are responsible for initiating the synthesis of plasmid and bacteriophage DNA. The oriC nucleotide sequence binds several units of the tetrameric form of the dnaA protein. This protein is named for the gene that encodes it. The dnaB and dnaC proteins then bind to the complex. As a result of binding these proteins, a portion of the helical DNA is unwound. This forces the rest of the DNA into a left-handed double helix that wraps around the proteins to give a structure... 

DNA very efficiently into their host bacteria. A single bacteriophage DNA can be replicated approximately 100-fold or more per cell depending on the type of phage and its host. 

Temperature jump studies on the binding dynamics of 5 with ct-DNA and T2 Bacteriophage DNA showed two lifetimes in the relaxation kinetics.117 The observed... 

The non-linear dependence of the relaxation process on the DNA concentration was also observed in stopped-flow experiments and the same mechanism, i.e. fast pre-equilibrium followed by a slow intercalation step, was proposed." This latter study did not report values for the individual rate constants. The mechanism proposed in Scheme 4 was employed in subsequent studies despite the criticism on the accuracy for the data related to the fast kinetic component (see below). The original temperature jump study also showed that the relaxation kinetics depend on the structure of the DNA.117 The slower intercalation rate for 5 with T2 Bacteriophage DNA when compared to ct-DNA was ascribed to the glucosylation of the former DNA (Table 3). 

Colomer-Lluch M, Jofre J, Muniesa M (2011) Antibiotic resistance genes in the bacteriophage DNA fraction of environmental samples. PLoS One 6(3) el7549... 

Hawkins RB (1978) Quantitative determination of cross-linkage of bacteriophage DNA and protein by ionizing radiation. Int J Radiat Biol 33 425-441... 

Double-stranded M13mp2 bacteriophage DNA transferred to E. coli Forward mutations No data + Snow 1991 Snow and Xu 1989 Chromium trichloride... 

In addition, three enzymes involved in DNA replication, including DNA primases, prokaryotic DNA topoisomerase I and some hexameric DNA helicases, are also classic zinc-ribbon proteins. In bacteriophage DNA primases, mutations of the zinc-binding residues abrogate the synthesis of RNA primers for lagging strand DNA synthesis. Strikingly, each subunit of the mini-chromosomal maintenance (MCM) protein, a heterohexameric helicase that initiates DNA replication in S. cerevisiae, contains an independently folded zinc-ribbon domain that appears to stabilize the dodecameric structure (a dimer of hexamers) of this replication complex. ... 

Each deflection has been plotted against a known composition (abundance) of bases, and standard curves have been prepared for the four common DNA bases. The sensitivity of the method has been established to subnanogram levels, assuming that all spectra are recorded under identical conditions (pyrolysis time, temperature, etc.) and on relatively pure DNA. Although the BH ions are unique and there is no interference from the nucleoprotein peaks, the Wiebers curves work well only for bacteriophage DNA they fail when tested on DNA obtained from other sources. 

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