U.S. RESEARCH ROUNDUP-Goldman Sachs, Yahoo, Terex

Sept 9 (Reuters) - Wall Street securities analysts revised their ratings and price targets on several U.S.-listed companies, including Medidata Solutions, Keycorp and Yahoo, on Wednesday. HIGHLIGHTS * Goldman Sachs : BofA Merrill raises to buy from neutral * Tetraphase Pharmaceuticals : Nomura, Brean, Stifel cuts rating on the stock * Terex Corp : JP Morgan cuts to underweight from neutral * Yahoo Barclays, Nomura, Mizuho, others cut target price * Ciena Corp : RBC