LAist, a local news offshoot of New York-based DNAinfo’s Gothamist website, has been shut down by billionaire Joe Ricketts, DNAinfo’s chief executive officer. Gothamist also has been discontinued.

The shutdown also included DNAinfo and local news sites Chicagoist, SFist, DCist and Shanghaiist.

Reporters and editors working in the combined DNAinfo and Gothamist newsroom voted last week to join the Writers Guild of America East. Newsroom employees at other websites under the DNAInfo umbrella had not joined a union when they were discontinued.

Ricketts, former chairman and chief executive of TD Ameritrade, founded DNAInfo in 2009 and acquired Gothamist and the associated websites earier this year. He posted a letter to readers on all of the sites Thursday addressing the shutdowns. All the rest of the content on the sites has been removed.

In the letter, Ricketts said the sites had “informed, impacted, and inspired millions of people” with their product. “I believe we’ve left the world a better place,” he said.

“But DNAInfo is, at the end of the day, a business, and businesses need to be economically successful if they are to endure,” Ricketts continued. “I’m hopeful that in time, someone will crack the code on a business that can support exceptional neighborhood storytelling, for I believe telling those stories remains essential.”

Contact media and entertainment reporter Diane Haithman at Follow her on Twitter @dhaithman for the latest in L.A. business news.