Wall Street opens flat as Yellen's speech awaited

Yellen is due to speak at an event hosted by Harvard University at 1:15 p.m. ET (1715 GMT). A rate hike in June was seen as highly unlikely until recently. "We're expecting a lot of major data in the next few weeks and Yellen will balance her comments keeping that in view," said Nadia Lovell, U.S. equity specialist at J.P. Morgan Private Bank in New York.