Gazprom and the government have long had a close relationship , but the revolving door between them is spinning especially fast this year : Mr. Medvedev , 42 , replaces Mr. Putin as president ; Mr. Putin becomes prime minister , replacing Viktor A. Zubkov ; and Mr. Zubkov is expected to take Mr. Medvedev 's place as Gazprom 's chairman at a general shareholders meeting in June .