ATP-dependent G-quadruplex unfolding by Bloom helicase exhibits low processivity

Various helicases and single stranded DNA (ssDNA) binding proteins unfold G-quadruplex (GQ) structures. However, the underlying mechanisms of this activity have only recently come to focus. We report kinetic studies on Bloom (BLM) helicase and human telomeric GQ interactions using single-molecule Förster resonance energy transfer (smFRET). Using partial duplex DNA (pdDNA) constructs with different 5' ssDNA overhangs, we show that BLM localizes in the vicinity of ssDNA/double-stranded DNA (dsDNA) junction and reels in the ssDNA overhang in an ATP-dependent manner. A comparison of DNA constructs with or without GQ in the overhang shows that GQ unfolding is achieved in 50-70% of reeling attempts under physiological salt and pH conditions. The unsuccessful attempts often result in dissociation of BLM from DNA which slows down the overall BLM activity. BLM-mediated GQ unfolding is typically followed by refolding of the GQ, a pattern that is repeated several times before BLM dissociates from DNA. BLM is significantly less processive compared to the highly efficient GQ destabilizer Pif1 that can repeat GQ unfolding activity hundreds of times before dissociating from DNA. Despite the variations in processivity, our studies point to possible common patterns used by different helicases in minimizing the duration of stable GQ formation.

Intervention research in occupational safety and health: examples from construction

Construction is one of the largest industries in the United States, with 13% of the gross national product and 5-6% of the labor force. It is also one of the most dangerous industries, accounting for 15% of occupational fatalities and 17% of all workers' compensation costs. In 1989, the Building and Construction Trades Department, AFL-CIO, completed an agreement with the National Institute for Occupational Safety and Health to develop a national labor-management initiative to improve occupational safety and health throughout the construction industry. The aim was to remedy a lack of research on construction occupational safety and health. The first years were spent on surveillance to characterize construction safety and health problems, development of awareness about safety and health issues among decisionmakers in the industry, and some limited interventions. A second phase was initiated in 1994, which focuses on intervention activities. Results from this joint program include a growth in annual federal construction safety and health research expenditure from $300,000 in 1989 to $12 million in 1995, a research network that now encompasses more than 30 institutions, a national conference that established an agenda to change construction safety and health, four regional conferences to develop coalitions and implementation strategies, and the development of a feasible goal to reduce fatality and injury rates by 80%. The program may already be having an impact. According to the Bureau of Labor Statistics, lost-time injury rates for construction for the three most recent years of reporting declined by 20%.