Shah Rukh Khan is leaving no stone unturned to make RA.One a superhit. After Rajinikanth, it’s Amitabh Bachchan who has become part of King Khan’s ambitious sci-fi film. But there is little twist Big B will only lend his voice and not act in the flick. According to a source, “SRK wanted Big B to do the voice over for an extremely important sequence in the film. Anubhav Sinha, the director was also keen on having someone to do the voice over. In fact, when Khan approached Bachchan, the superstar immediately agreed to be a part of the superhero flick. There is immense respect between SRK and Amitji”.RA.One's director Anubhav Sinha confirmed the news to Mumbai Mirror, “Amitji has been kind enough. We needed someone special to do this voiceover in the film. Also, the project will now get blessings from the people we have loved and respected for years. God is kind to me. I had SRK, Arjun Rampal, Kareena Kapoor, Priyanka Chopra and Sanjay Dutt. Now I even have Rajinikanth sir and Mr Amitabh Bachchan in my film. I feel blessed.”Other actor who're playing cameos just for SRK1) Rajinikanth as Chitti: Shah Rukh had to increase RA.One's budget to accommodate Rajinikanth's creative suggestions.2) Sanjay Dutt will play Khalnayak and has shot for an action sequence.3) Priyanka Chopra will portray The Damsel in Distress.