BUZZ-Sage rises after Biogen proposes to buy remaining stake for $442 mln

** Shares of drugmaker Sage Therapeutics SAGE.O rise 36.4% to $7.57 premarket

** Drugmaker Biogen BIIB.O will buy all outstanding shares of Sage that it does not already own for $7.22 apiece, a filing showed on Friday

** The offer price, representing a 30% premium to stock's close on Friday, values Sage's equity at $441.7 mln, according to Reuters calculations

** Brokerage William Blair says the offer is prudent to maximize potential for Sage and Biogen's depression drug, Zurzuvae, without materially impacting Biogen's M&A deal capacity

** Up to last close, stock down 78.1% in the last 12 months

(Reporting by Christy Santhosh)

((Christy.Santhosh@thomsonreuters.com))