Wall Street ends lower after Yellen comments fail to inspire

U.S. stocks ended weaker on Friday after Federal Reserve Chair Janet Yellen indicated that the central bank was poised to raise interest rates this year, in line with Wall Street's expectations. In a speech, Yellen said a rate hike would be warranted this year if the economy keeps improving as expected. Investors have enjoyed an extended period of low volatility and steady gains, but with the Fed on track to raise rates this year and major indexes near records, the market could get a bit ch