Nikolai Lashkevich said Prana made a final payment of 95.68 billion rubles (about $3.7 billion) into a Yukos account on May 29.
At the May 11 auction for Yukos's high-tech 22-story building in downtown Moscow with 29,000 square meters (87,000 square feet) of floorspace, along with a host of research assets, Prana outbid a subsidiary of state-controlled oil giant Rosneft by raising the initial price by more than 300%.
The Russian anti-monopoly service earlier said it would block Prana's deal until its ownership structure was clarified, but allowed Prana on May 28 to make the purchase.
Igor Artemyev, the head of the anti-monopoly service, said earlier Wednesday that the competition regulator was aware of the ownership structure of Prana, but declined to specify it.