https://cancerbiologyprogram.med.wayne.edu/pdfs/hallmarks_cancer_article.pdf

Hallmarks of cancer: the next generation.

We describe an isothermal, single-reaction method for assembling multiple overlapping DNA molecules by the concerted action of a 5' exonuclease, a DNA polymerase and a DNA ligase. First we recessed DNA fragments, yielding single-stranded DNA overhangs that specifically annealed, and then covalently joined them. This assembly method can be used to seamlessly construct synthetic and natural genes, genetic pathways and entire genomes, and could be a useful molecular engineering tool.

/pdf/enzymatic-assembly-of-dna-molecules-up-to-several-hundred-3ay6wri4tz.pdf

Enzymatic assembly of DNA molecules up to several hundred kilobases

▪ Abstract The innate immune system is a universal and ancient form of host defense against infection. Innate immune recognition relies on a limited number of germline-encoded receptors. These receptors evolved to recognize conserved products of microbial metabolism produced by microbial pathogens, but not by the host. Recognition of these molecular structures allows the immune system to distinguish infectious nonself from noninfectious self. Toll-like receptors play a major role in pathogen recognition and initiation of inflammatory and immune responses. Stimulation of Toll-like receptors by microbial products leads to the activation of signaling pathways that result in the induction of antimicrobial genes and inflammatory cytokines. In addition, stimulation of Toll-like receptors triggers dendritic cell maturation and results in the induction of costimulatory molecules and increased antigen-presenting capacity. Thus, microbial recognition by Toll-like receptors helps to direct adaptive immune responses ...

/pdf/innate-immune-recognition-3eedeqyq83.pdf

Innate Immune Recognition

Poly(ADP-ribose) polymerase (PARP1) facilitates DNA repair by binding to DNA breaks and attracting DNA repair proteins to the site of damage. Nevertheless, PARP1-/- mice are viable, fertile and do not develop early onset tumours. Here, we show that PARP inhibitors trigger gamma-H2AX and RAD51 foci formation. We propose that, in the absence of PARP1, spontaneous single-strand breaks collapse replication forks and trigger homologous recombination for repair. Furthermore, we show that BRCA2-deficient cells, as a result of their deficiency in homologous recombination, are acutely sensitive to PARP inhibitors, presumably because resultant collapsed replication forks are no longer repaired. Thus, PARP1 activity is essential in homologous recombination-deficient BRCA2 mutant cells. We exploit this requirement in order to kill BRCA2-deficient tumours by PARP inhibition alone. Treatment with PARP inhibitors is likely to be highly tumour specific, because only the tumours (which are BRCA2-/-) in BRCA2+/- patients are defective in homologous recombination. The use of an inhibitor of a DNA repair enzyme alone to selectively kill a tumour, in the absence of an exogenous DNA-damaging agent, represents a new concept in cancer treatment.

Specific killing of BRCA2-deficient tumours with inhibitors of poly(ADP-ribose) polymerase

Whether and how human tumours are genetically unstable has been debated for decades. There is now evidence that most cancers may indeed be genetically unstable, but that the instability exists at two distinct levels. In a small subset of tumours, the instability is observed at the nucleotide level and results in base substitutions or deletions or insertions of a few nucleotides. In most other cancers, the instability is observed at the chromosome level, resulting in losses and gains of whole chromosomes or large portions thereof. Recognition and comparison of these instabilities are leading to new insights into tumour pathogenesis.

Genetic instabilities in human cancers

A critical role for histone H2AX in recruitment of repair factors to nuclear foci after DNA damage.

In 1910, Bang' reported that concentrated solutions of guanylic acid formed a gel. We have also observed that concentrated solutions (25.0 mg/ml) of guanylic acid (GMP) at pH 5 are extremely viscous and, if cooled, form a clear gel. Less concentrated solutions also gel on cooling but assume a more normal viscosity at room temperature. From examination of the optical properties of the gel and investigation of the structure of fibers obtained from the gel by drying, we have concluded that, at least in the case of the 5' isomer, the phenomenon may be explained as being due to helix formation by the guanylic acid. A possible structure is presented for this helix.

https://www.pnas.org/content/pnas/48/12/2013.full.pdf

Helix Formation by Guanylic Acid

Relaxed closed-circular DNA is converted to negatively supercoiled DNA by DNA gyrase. This enzyme has been purified from Escherichia coli cells. The reaction requires ATP and Mg++ and is stimulated by spermidine. The enzyme acts equally well on relaxed closed-circular colicin E1, phage lambda, and simian virus 40 DNA. The final superhelix density of the DNA can be considerably greater than that found in intracellularly supercoiled DNA.

https://www.pnas.org/content/pnas/73/11/3872.full.pdf

DNA gyrase: an enzyme that introduces superhelical turns into DNA

The 3′ to 5′ Exonuclease Activity of Mre11 Facilitates Repair of DNA Double-Strand Breaks

ATP-dependent DNA supercoiling catalyzed by Escherichia coli DNA gyrase was inhibited by oxolinic acid, a compound similar to but more potent than nalidixic acid and a known inhibitor of DNA replication in E. coli. The supercoiling activity of DNA gyrase purified from nalidixic acid-resistant mutant (nalAR) bacteria was resistant to oxolinic acid. Thus, the nalA locus is responsible for a second component needed for DNA gyrase activity in addition to the component determined by the previously described locus for resistance to novobiocin and coumermycin (cou). Supercoiling of λ DNA in E. coli cells was likewise inhibited by oxolinic acid, but was resistant in the nalAR mutant. The inhibition by oxolinic acid of colicin E1 plasmid DNA synthesis in a cell-free system was largely relieved by adding resistant DNA gyrase. 

In the absence of ATP, DNA gyrase preparations relaxed supercoiled DNA; this activity was also inhibited by oxolinic acid, but not by novobiocin. It appears that the oxolinic acid-sensitive component of DNA gyrase is involved in the nicking-closing activity required in the supercoiling reaction. In the presence of oxolinic acid, DNA gyrase forms a complex with DNA, which can be activated by later treatment with sodium dodecyl sulfate and a protease to produce double-strand breaks in the DNA. This process has some similarities to the known properties of relaxation complexes.

https://www.pnas.org/content/pnas/74/11/4772.full.pdf

Martin Gellert

Papers

A critical role for histone H2AX in recruitment of repair factors to nuclear foci after DNA damage.

Helix Formation by Guanylic Acid

DNA gyrase: an enzyme that introduces superhelical turns into DNA

The 3′ to 5′ Exonuclease Activity of Mre11 Facilitates Repair of DNA Double-Strand Breaks

Nalidixic acid resistance: A second genetic character involved in DNA gyrase activity