Shares of Sterling Financial Corp. (Nasdaq: STSA) were up as much as 33 percent today after it was announced that private-firm, Warburg Pincus would invest $139 million to support the bank’s recapitalization plan.

If the deal goes through, Warburg Pincus would own about 20 percent of Sterling’s common stock. The investment would augment last month’s announcement that Thomas H. Lee Partners (THL) of Boston will invest $134.7 million in the struggling Spokane bank if certain conditions are met.

As part of the Warburg Pincus investment, Thomas H. Lee Partners agreed to adjust the size of its previously announced proposed investment to equal the Warburg Pincus investment. Upon the closing of the recapitalization transactions, the two firms would invest a total of $278 million combined, and would hold an ownership stake of about 40% of Sterling Financial.

“We are pleased to announce Warburg Pincus as an investor in Sterling,” said Sterling’s president and CEO, Greg Seibly. “Warburg Pincus is a highly successful bank sector investor that has long-standing and deep knowledge of our company.”

Sterling Financial Corporation of Spokane, Wash., is the bank holding company for Sterling Savings Bank, a commercial bank, and Golf Savings Bank, a savings bank focused on single-family mortgage originations.