The bank said it plans to use proceeds from the placement to expand its operations.
The Texas company will gain four branches and $160 million in loans after the acquisition closes.
The private-equity firms, which invested in a predecessor to Union Bancshares in May 2010, sold their shares for a total of $301 million.
Ameris would gain 24 Atlanta-area branches in the $406 million deal.
Marathon International Bank would target the Ethiopian community with specific advertising and educational programs.
NewDominion, which has completed an improbable turnaround, is the last community bank based in Charlotte, N.C.
The company sold common stock to employees, existing shareholders and new investors.
Organizers of Sterling Bank have filed an application with the FDIC and have set a $20 million capital target.
The company will pay $62 million in cash for a bank with four branches and $337 million in assets.
Endeavor Bank, which raised nearly $27 million, will become the second new bank to open in California in the past year when it debuts next week.
