WASHINGTON, Aug 31 (Reuters) - U.S. President Donald Trump will nominate Columbia University law professor Robert Jackson to be a member of the Securities and Exchange Commission, a person with knowledge of the matter said on Thursday.

Jackson is expected to be formally nominated on Friday, the source said. He would fill a vacant spot reserved for a Democrat on the five-member panel. (Reporting by Svea Herbst-Bayliss; Writing by Eric Beech; Editing by Mohammad Zargham)