The General Motors Foundation awarded a $1 million grant to Lonnie G. Bunch, founding director of the Smithsonian’s National Museum of African American History and Culture, at the Washington Auto Show, the museum announced Thursday.

The gift makes the GM Foundation a founding donor to the museum, which is under construction on five acres adjacent to the Washington Monument and scheduled to open in late 2015. Other prominent museum donors include media titan Oprah Winfrey, who has donated $13 million and whose name will go on a 350-seat theater in recognition; the Bill and Melinda Gates Foundation; and American Express.

In 2012, ground was broken on the $500 million museum — a cost to be evenly split between public and private funds. About $400 million has been raised so far, according to a museum representative.

“Through this grant we continue our commitment by helping to bring to life the story of African Americans who have changed our nation in so many ways,” said the foundation’s president, Vivian Pickard, in a statement. The organization was also a founding donor to the National Museum of American History’s 2003 exhibition “America on the Move.”

Bunch said he had been talking to the GM Foundation for about a year. “We just continued to have a conversation about what the museum was trying to do,” he said. The donation will support the design and installation of the museum’s permanent exhibition and help construction stay on schedule.

In November, a Jim Crow-era railcar and a 1930s guard tower from the Louisiana State Penitentiary became the first artifacts installed in the museum.

“This is an extremely important experience and endeavor, and it is important that corporations who care about diversity and history should be part of this,” Bunch said.

Bunch said he is happy about the grant but added: “I jump up and down every time we get a donation, whether it’s $5 or $5 million. What I realize is, every donation is a step closer to making dreams of our ancestors real. That excites me every moment.”