What happens when one of the nation's biggest content distributors tries to buy one of the nation's big content producers? Thanks to the Comcast/NBC deal, we now know the answer: the Department of Justice takes a magnifying glass to the deal.

The DOJ has just announced its plan to review the buyout for antitrust problems. Comcast already presides over a massive empire that includes its flagship cable network and a host of other properties like Fancast, movie ticket site Fandango, social networking site Plaxo, five TV networks including E!, G4, and Style, along with a couple of pro sports teams and a skating production company.

The deal with NBC Universal would expand the company's distribution reach (through local NBC affiliates) but would more importantly give it control of a major producer of TV and movie content.

The FCC will also weigh in on the deal, and Comcast will certainly be subjected to a host of conditions by both agencies if the deal is approved. The DOJ has been far more focused on antitrust issues over the last year, and the FCC has a history of applying rules to such major deals. When AT&T bought BellSouth a few years back, Democratic commissioners held out for concessions and did force the company to support net neutrality for three years, offer low-cost starter DSL service, and make other changes deemed to be "in the public interest."