US STOCKS-Wall Street opens lower as oil prices drop
* Fed Chair Yellen to speak at Jackson Hole on Friday
* Oil prices drop 3 pct; dollar rises for second day
* Medivation jumps on $14 bln Pfizer deal
* Indexes down: Dow 0.46 pct, S&P 0.36 pct, Nasdaq 0.25 pct (Updates to open)
By Yashaswini Swamynathan
Aug 22 (Reuters) - Wall Street opened lower on Monday as oil prices dropped the most in four weeks and investors weighed the prospects of an interest rate hike in the coming months.
Oil prices fell nearly 3 percent as China ramped up exports of refined products, U.S. producers added rigs for an eighth consecutive week, and prospects emerged for increased exports from Iraq and Nigeria.
With the earnings season coming to an end, investor focus will shift to Federal Reserve Chair Janet Yellen's speech on Friday at the annual central bankers' meeting in Jackson Hole, Wyoming.
"The markets will start to get a little bit nervous about what's going to be said, what kind of indications will be given about a September hike," said Robert Pavlik, chief market strategist at Boston Private Wealth in New York. Continuación...