Background: HDHB has been implicated in chromosomal replication, but its role has not been determined. Results: Replication stress recruits HDHB to chromatin in a checkpoint-independent, RPA-dependent manner, and HDHB silencing reduces recovery from replication stress. Conclusion: HDHB functions in chromosomal replication to relieve replication stress. Significance: HDHB competition with checkpoint-signaling proteins for binding to RPA may modulate cellular responses to replication stress.

Mutational studies of human DNA helicase B (HDHB) have suggested that its activity is critical for the G1/S transition of the cell cycle, but the nature of its role remains unknown. In this study, we show that during G1, ectopically expressed HDHB localizes in nuclear foci induced by DNA damaging agents and that this focal pattern requires active HDHB. During S and G2/M, HDHB localizes primarily in the cytoplasm. A carboxy-terminal domain from HDHB confers cell cycle-dependent localization, but not the focal pattern, to a reporter protein. A cluster of potential cyclin-dependent kinase phosphorylation sites in this domain was modified at the G1/S transition and maintained through G2/M of the cell cycle in vivo, coincident with nuclear export of HDHB. Serine 967 of HDHB was the major site phosphorylated in vivo and in vitro by cyclin-dependent kinases. Mutational analysis demonstrated that phosphorylation of serine 967 is crucial in regulating the subcellular localization of ectopically expressed HDHB. We propose that the helicase of HDHB operates primarily during G1 to process endogenous DNA damage before the G1/S transition, and it is largely sequestered in the cytoplasm during S/G2.

Homologous recombination is involved in the repair of DNA damage and collapsed replication fork, and is critical for the maintenance of genomic stability. Its process involves a network of proteins with different enzymatic activities. Human DNA helicase B (HDHB) is a robust 5′-3′ DNA helicase which accumulates on chromatin in cells exposed to DNA damage. HDHB facilitates cellular recovery from replication stress, but its role in DNA damage response remains unclear. Here we report that HDHB silencing results in reduced sister chromatid exchange, impaired homologous recombination repair, and delayed RPA late-stage foci formation induced by ionizing radiation. Ectopically expressed HDHB colocalizes with Rad51, Rad52, RPA, and ssDNA. In vitro, HDHB stimulates Rad51-mediated heteroduplex extension in 5′-3′ direction. A helicase-defective mutant HDHB failed to promote this reaction. Our studies implicate HDHB promotes homologous recombination in vivo and stimulates 5′-3′ heteroduplex extension during Rad51-mediated strand exchange in vitro.

Quaternary compounds Cu 2 FeSnS 4 (CFTS), a promising alternative material for solar cell absorber layer, were successfully synthesised by a liquid reflux method in a mixture solvent of triethylenetetramine-ethylene glycol (TETA-EG, 1:1, v/v) at 230°C for 3 h under the atmospheric pressure condition. The phase, micro-structure, morphology, chemical composition and optical properties of the as-synthesised CFTS micro/ nano particles were characterised using X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectrometry and ultravioletvisible absorption spectrophotometer. The results showed that the stannite structured CFTS micro/nano particles with close to theoretical stoichiometric ratio were pure and well-crystallised, the particle size ranged from 70 to 240 nm and the particles were well-distributed, the band gap was about 1.25 eV which indicated its suitable application as the absorption layer of thin film solar cells.

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