Knockouts of RecA-Like Proteins RadC1 and RadC2 Have Distinct Responses to DNA Damage Agents in Sulfolobus islandicus

RecA family recombinases play essential roles in maintaining genome integrity. A group of RecA-like proteins named RadC are present in all archaea, but their in vivo functions remain unclear. In this study, we performed phylogenetic and genetic analysis of two RadC proteins from Sulfolobus islandicus. RadC is closer to the KaiC lineage of cyanobacteria and proteobacteria than to the lineage of the recombinases （RecA, RadA, and Rad51） and the recombinase paralogs （e.g., RadB, Rad55, and Rad51B）. Using the recently- established S. islandicus genetic system, we constructed deletion and over-expression strains of radC1 and radC2. Deletion of radC1 rendered the cells more sensitive to DNA damaging agents, methyl methanesulfonate （MMS）, hydroxyurea （HU）, and ultraviolet （UV） radiation, than the wild type, and a AradCIAradC2 double deletion strain was more sensitive to cisplatin and MMS than the AradC1 single deletion mutant. In addition, ectopic expression of His-tagged RadC 1 revealed that RadC I was co-purified with a putative structure-specific nuclease and ATPase, which is highly conserved in archaea. Our results indicate that both RadCI and RadC2 are involved in DNA repair. RadCl may play a general or primary role in DNA repair, while RadC2 plays a role in DNA repair in response to specific DNA damages.

Manipulation and detection of single nanoparticles and biomolecules by a photonic nanojet

Optical methods to manipulate and detect nanoscale objects are highly desired in both nanomaterials and molecular biology fields.Optical tweezers have been used to manipulate objects that range in size from a few hundred nanometres to several micrometres.The emergence of near-field methods that overcome the diffraction limit has enabled the manipulation of objects below 100 nm.A highly free manipulation with signal-enhanced real-time detection,however,remains a challenge for single sub-100-nm nanoparticles or biomolecules.Here we show an approach that uses a photonic nanojet to perform the manipulation and detection of single sub-100-nm objects.With the photonic nanojet generated by a dielectric microlens bound to an optical fibre probe,three-dimensional manipulations were achieved for a single 85-nm fluorescent polystyrene nanoparticle as well as for a plasmid DNA molecule.Backscattering and fluorescent signals were detected with the enhancement factors up to~103 and~30,respectively.The demonstrated approach provides a potentially powerful tool for nanostructure assembly,biosensing and single-biomolecule studies.