WASHINGTON: Genentech chairman Arthur Levinson has resigned from the board of directors of Google amid a probe by US authorities into his membership of the boards of both the Internet giant and Apple.

Google, in a statement on Monday, did not give any reason for Levinson's decision to step down from the Google board but it comes just two months after Google chief executive Eric Schmidt resigned from the board of Apple.

US law prohibits a person's presence on the boards of two companies that are direct rivals, as it may affect competition between them, and the Federal Trade Commission opened an investigation in May into the overlapping Google and Apple board memberships and whether they posed any potential conflicts of interest.

Schmidt, asked by a reporter less than two weeks ago whether Levinson should step down from the board of Google, said "I would hope not. I don't think it's necessary."

Levinson had served on the Google board since April 2004.

Schmidt on Monday described Levinson as a good friend and valued colleague.

"Art has been a key part of Google's success these past five years, offering unvarnished advice and vital counsel on every big issue and opportunity Google has faced," Schmidt said. "Though he leaves as a member of our Board, Art will always have a special place at Google."

Levinson said working with Google has been a "remarkable experience."

"I greatly admire what they've built and have no doubt that Google has a terrific future," he said.

Apple chief executive Steve Jobs, in announcing Schmidt's resignation from the Apple board in August, said the Google CEO could no longer function effectively with Google entering more of Apple's core businesses, such as the smartphone and personal computer operating system markets.