Activist investor Jana Partners LLC disclosed a 5.8 percent stake in natural gas producer EQT Corp (EQT.N) on Monday and urged the company to abandon its $6.7 billion buyout of rival Rice Energy Inc (RICE.N). The move, which threatens to scuttle EQT's plans to become the largest U.S. natural gas producer, is hedge fund Jana's latest foray into the energy sector. Jana pushed Oil States International Inc (OIS.N) to spin off Civeo Corp (CVEO.N) in 2014. Jana began buying shares in April before the Rice deal was announced last month and has become EQT's fourth-largest shareholder. It said in regulatory...