* Futures off: Dow 34 pts, S&P 6.25 pts, Nasdaq 14.25 pts
By Chuck Mikolajczak
NEW YORK, Sept 22 (Reuters) - Sigma-Aldrich shares were surging on Monday, up 34.4 percent to $137.60 after German drugs and chemicals maker Merck KGaA said on Monday it agreed to acquire Sigma-Aldrich for $17 billion in cash to boost its life science business.
Volume of over 208,000 shares made it the second-most active Nasdaq listed stock in premarket and was more than 60 percent of its day-average volume of about 334,000.
Also on the Nasdaq, Yahoo shares were trading down 2.5 percent to $39.89 as the most actively traded stock on the exchange before the opening bell. The stock was downgraded by Bank of America Merrill Lynch and Bernstein in the wake of the Alibaba Group debut on Friday.
Dresser-Rand shares were up 2.1 percent to $81.61 in premarket after Germany's Siemens agreed to buy Dresser-Rand, a U.S. oilfield equipment maker, for $7.6 billion in cash. The stock rallied more than 17 percent last week in anticipation of the deal. Consolidated volume of over 600,000 shares made Dresser-Rand the second most actively traded NYSE issue.
U.S. stock index futures were falling on Monday, putting the S&P 500 on track to pull back from near-record levels after China's finance minister indicated the country will not increase stimulus measures and ahead of data on the housing market.
China will not dramatically alter its economic policy because of any one economic indicator, Finance Minister Lou Jiwei said on Sunday, in remarks that came days after many economists lowered growth forecasts having seen the latest set of weak data.
U.S. existing home sales data for August is due at 10 a.m. (1400 GMT). Expectations call for existing home sales to increase to an annual rate of 5.2 million units versus 5.15 million in July.
* S&P 500 e-minis were falling 6.25 points, or 0.31 percent, with 164,028 contracts changing hands.
* Nasdaq 100 e-minis were down 14.25 points, or 0.35 percent, in volume of 26,323 contracts.
* Dow e-minis were down 34 points, or 0.2 percent, with 29,743 contracts changing hands. (Reporting by Chuck Mikolajczak; Editing by Chizu Nomiyama)