A few names long associated with old-school television are partnering to chase a very new-media trend: vertical video series. BET , the Paramount-owned media group focused on the Black community and best known for its basic cable channel, revealed on Wednesday that it is partnering with microdrama company aTwist to develop and distribute these series, also known as verticals, across both linear and digital platforms. Formerly called MicroCo, aTwist was founded by former WME and ABC Entertainment head Lloyd Braun, ex-Showtime president Jana Winograde, and former NBCUniversal Television and Streaming entertainment chairwoman Susan Rovner . The deal essentially provides a declining cable asset with low-cost programming while offering aTwist projects greater visibility and an additional revenue window. Through the partnership, BET and aTwist will produce series that can be viewed on cable television as well as on aTwist’s forthcoming mobile app, which is set to launch this summer.…