Under the regulatory spotlight, another link between the historically close top brass at Google an Apple was broken today, further preparing the ground for a more intense rivalry between the two.

Arthur Levinson, former chief executive of biotech giant Genentech, resigned his non-executive seat on the Google board, which he has held since 2004. He'll continue in a similar role up the road at Apple however.

Steve Jobs blamed Schmidt's departure on Google treading on his firm's toes with Chrome OS and Android. The Federal Trade Commission had also in May announced an investigation of whether the ties between Apple and Google violated anti-trust laws.

Levinson's resignation today ends the crossover between the two boards. The decision was apparently a quick one; asked last week if Levinson should quit, Schmidt said: "I would hope not... because I don't think it's necessary."

Levinson evidently disagreed, or was advised to disagree, and Apple and Google's boards - formerly united by antipathy towards Microsoft - are now free to do battle over the browser, operating system and smartphone markets.

As if to illustrate the growing enmity, the pair have recently been involved in an ugly public spat over the rejection of the Google Voice app for the iPhone. ®

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