Vince Cable will play no further part in the decision on News Corporation's proposed takeover of BSkyB following indiscreet comments about Rupert Murdoch.
The Business Secretary's Department for Business, Innovation and Skills has been stripped of responsibility for media competition and policy issues, which are transferred to the Department of Culture, Media and Sport, headed by Jeremy Hunt.
But Mr Cable has saved his job, despite saying he was "at war" with Mr Murdoch in a secret recording made by the Daily Telegraph.
In a statement, Downing Street said that Mr Cameron made clear to Mr Cable that his comments were "totally unacceptable and inappropriate".
A No 10 spokesman said: "Following comments made by Vince Cable to the Daily Telegraph, the Prime Minister has decided that he will play no further part in the decision over News Corporation's proposed takeover of BSkyB.
"In addition, all responsibility for competition and policy issues relating to media, broadcasting, digital and telecoms sectors will be transferred immediately to the Secretary of State for Culture, Media and Sport.
"This includes full responsibility for Ofcom's activities in these areas.
"The Prime Minister is clear that Mr Cable's comments were totally unacceptable and inappropriate."
Mr Cable said in a statement: "I fully accept the decision of the Prime Minister and Deputy Prime Minister. I deeply regret the comments I made and apologise for the embarrassment that I have caused the Government."
Shadow business secretary John Denham said: "David Cameron has decided to hang on to a lame duck Business Secretary who has no credibility.
"Vince Cable has been removed from one of the most important decisions in the department. He has revealed how the Government is paralysed by infighting. And he has failed to produce a plan for growth.
"The only reason for holding on to him is to keep the sagging tent of this Tory-led Government upright but at the expense of British business."