UPDATE 1-Ex-Genentech boss Levinson resigns from Roche's board

* Levinson CEO of Google’s Calico since Sept. 2013

* Move comes day after Calico deal with AbbVie

* Departure a “loss” for Roche - analyst (Amends slug, adds details on AbbVie Calico deal, analyst)

ZURICH, Sept 4 (Reuters) - Swiss drugmaker Roche said on Thursday that Art Levinson had resigned from its board of directors with immediate effect, in order to avoid any conflict of interest given his role as chief executive at Google’s Calico.

The move comes a day after Calico partnered with Roche’s rival AbbVie Inc to invest in new research operations for age-related diseases.

Levinson, 64, is a former chief executive and guiding force behind Genentech, a cancer company considered by many to be the most successful biotechnology company in history.

He stepped down as CEO after Roche bought out the remaining stake it did not already own in the U.S. group for $47 billion in 2009, but became a board member at the Swiss drugmaker.

Fabian Wenner, an analyst at Kepler Cheuvreux in Zurich said it was a shame Roche had not been able to keep hold of a person with extensive sector experience and a strong track record.

“Apart from Art, there’s only one board member now with sector experience which is quite a loss for Roche in my view,” he said. “The fact the Calico partnered with AbbVie and not with Roche is not a good indicator.”

Levinson, who is also chairman of Apple, has a high-calibre network and has already poached several heavy-hitters to join Google’s nascent biotech company, including Hal Barron, Roche’s former chief medical officer, who joined Calico last year.

“We regret Art’s decision but at the same time understand his reasons,” said Roche Chairman Christoph Franz in a statement.

Levinson was passed over for the role of Roche chairman in favour of Franz, a former CEO of German airline Lufthansa who took up the job in March. (Additional reporting by Joshua Franklin; Editing by Clarence Fernandez and Mark Potter)