SAN FRANCISCO -- An Oakland medical marijuana dispensary that has been billed as the largest pot shop on the planet has been targeted for closure by federal prosecutors in Northern California, suggesting that a crackdown on the state's medical marijuana industry remains well under way.U.S. Attorney Melinda Haag has threatened to seize the Oakland property where Harborside Health Center has operated since 2006, as well as its sister shop in San Jose, executive director and co-founder Steve DeAngelo said Wednesday.