AT&T has implemented a massive overhaul of WarnerMedia’s senior management team, bringing major structural changes to HBO, Turner and Warner Bros. as it looks to streamline operations and ramp up original content for the streaming era.

Former NBC Entertainment and Showtime chief Bob Greenblatt has signed on as chairman of WarnerMedia Entertainment and direct to consumer. He’ll oversee HBO and TNT, TBS, and TruTV as well as content for the streaming service planned to launch at year’s end. CNN chief Jeff Zucker, Warner Bros. chairman-CEO Kevin Tsujihara, and Turner International leader Gerhard Zeiler are also gaining more turf in the reorganization.

The shakeup comes nearly nine months after AT&T closed its $85.4 billion acquisition of Time Warner. Although AT&T leaders were quick to praise the Time Warner’s seasoned executive team, changes were inevitable as HBO, Turner and Warner Bros. took on a new corporate parent. Company insiders are now bracing for layoffs amid the consolidation process.

Zucker is expanding his purview to include all sports under the WarnerMedia umbrella in the new role as chairman of WarnerMedia News and Sports. Turner Sports, Bleacher Report, and the AT&T Regional Sports Networks will fall under Zucker’s leadership alongside CNN Worldwide.

Cartoon Network, Adult Swim, Boomerang and Turner Classic Movies — four linear cablers that had been part of Turner — will be absorbed by Warner Bros., along with all animation production operations and consumer products. Warner Bros. will create a Global Kids and Young Adults unit to bring new focus to development content and related properties for kids and family audiences. Warner Bros. will also be the new home of Otter Media, the digital content investment venture that AT&T started with Peter Chernin prior to its acquisition of Time Warner.

Zeiler has been named chief revenue officer for WarnerMedia. He will oversee the combined HBO and Turner affiliate sales operation as well as all advertising sales efforts for the company.

“We have done an amazing job establishing our brands as leaders in the hearts and minds of consumers,” said John Stankey, WarnerMedia CEO. “Adding Bob Greenblatt to the WarnerMedia family and expanding the leadership scope and responsibilities of Jeff, Kevin and Gerhard — who collectively have more than 80 years of global media experience and success — gives us the right management team to strategically position our leading portfolio of brands, world-class talent and rich library of intellectual property for future growth.”

The changes mark a re-engineering of the corporate structure that held under Time Warner’s management of HBO, Turner and Warner Bros. for nearly 25 years.

Greenblatt’s impending appointment spurred the resignations last week of HBO chairman-CEO Richard Plepler and Turner president David Levy. The departures of both longtime executives will only reinforce the magnitude of the changes for HBO and Turner staffers.

Time Warner’s three core divisions had historically been run as separate fiefdoms, following Time Inc.’s merger with Warner Bros. in 1990 and Time Warner’s acquisition of Turner Broadcasting in 1996. Rumblings about fundamental changes at WarnerMedia began the day AT&T received the final green light for its Time Warner acquisition, when a federal appeals court upheld a lower court ruling allowing the deal to proceed despite the Justice Department’s effort to block it on antitrust grounds.

The new structure reinforces AT&T’s vision of bundling HBO and the former Turner channels as a streaming service offering augmented with original programming. WarnerMedia said the new focus was to organize operations around distinct disciplines: entertainment networks, live programming, content production and affiliate and advertising sales.

AT&T has made an enormous bet on Greenblatt to lead the bulk of its programming operations at a time when the battle for viewers has gone global and reached unprecedented heights in production expenditures. Greenblatt’s arrival has already jolted the HBO and Turner establishment with the exits of Plepler and Levy.

AT&T is clearly banking on Greenblatt’s track record in turning Showtime into an original programming powerhouse and in restoring luster to NBC during his eight-year tenure as chairman. Earlier in his career, Greenblatt was part of the early wave of Fox Broadcasting executives. During Greenblatt’s time as an independent producer — between the end of his Fox run and before he joined Showtime in 2003 — he and former partner David Janollari were executive producers with creator Alan Ball of HBO’s much-praised “Six Feet Under.”

“I’m honored to be joining WarnerMedia during such an exciting time for the company and the industry as a whole, and I look forward to working alongside the many talented executives and team members across the company,” Greenblatt said. “WarnerMedia is home to some of the world’s most innovative, creative and successful brands and we’re in a unique position to foster even deeper connections with consumers. And it goes without saying I will always have a soft spot in my heart for HBO going back to the rewarding experience I had producing Alan Ball’s ‘Six Feet Under.'”

The shuffling of assets to Warner Bros. is also a boon for Tsujihara, who has been CEO of the studio since early 2013. Zucker took the reins of CNN Worldwide in January 2013 after a long run at NBC. Zeiler joined Turner as head of international in February 2012, after serving as chief of Germany’s powerful RTL Group.

(Pictured: Bob Greenblatt, Jeff Zucker and Kevin Tsujihara)