Rick Rubin signs on as Columbia records exec -- The megaproducer heads a roster that includes Beyonce, Bob Dylan, and Bruce Springstein

It’s official: Rick Rubin — the legendary producer responsible for everything from pairing Aerosmith with Run-DMC to helping the Dixie Chicks sweep the Grammys last February — is joining Columbia Records in an executive partnership with company head Steve Barnett. He will head a roster full of big guns like Beyoncé, Bruce Springsteen, and Bob Dylan, though he’s also expected to continue working with outside acts. An internal memo at parent company Sony BMG — which claims more than a quarter of the current album market share — says Rubin’s hire will move Columbia ”to the forefront of artist development while building a new business model.” How that model will be structured is anyone’s guess, as rumors of mass firings, artist reshufflings, and even a total relocation to Sony BMG’s West Coast offices sparked instantly. (Rubin is staying in L.A.; Barnett is based in New York.) ”No one knows what’s going on,” confides one staffer. As for the day-to-day business of running the label? It’ll likely be a division of labor. Says an insider, ”Rick is all about the art, while Steve is all about the business. It’s a yin-yang thing.”