Nippon Life Insurance Co. has reached a deal to acquire 24.75 percent of U.S. investment firm TCW Group Inc. from U.S. asset manager Carlyle Group LP, the companies said recently.

While terms were not disclosed, a person with direct knowledge of the matter said the company, Japan's biggest private-sector life insurer, would pay about ¥55 billion ($488.37 million). Nippon Life and Carlyle declined to comment on the price.

Nippon Life, which will have two seats on TCW's board, said the transaction should close this month, pending regulatory approval.