Gatekeeping is a function of controlling information, which, in part determines who holds power via mass communication. This is due to gatekeeping being the determination of what appears in popular media via the selection of particular messages from otherwise countless sources of information.
The fact that popular news outlets are businesses helps keep gatekeeping alive. This is because those that own outlets like newspapers have a vested interest in printing information that is most likely to sell papers. With limited space within the newspaper pages, stories that are less likely to excite the public and sell papers are not printed. Thus, outlets like newspapers participate in gatekeeping by controlling the information published, allowing the commercially-interesting stories "through the gate" and giving them viability in the public eye.
Gatekeeping can be employed on a smaller scale by the writer of a story and on a larger scale by the editor of the story. This is because the writer makes his own choices regarding what he will write about and what narrative he will give, thus favoring certain stories and information over others. It is ultimately his editor who makes the decision to publish this story among others that are submitted. The editor controls the information given to the masses via these published stories, making his gatekeeping powers broader. In instances where the editor publishes his own stories, he obviously has even greater gatekeeping control.