For PSU recruitment through GATE, there may not be an exam in most cases except say NTPC. Shortlisting is on the basis of GATE scores only. The applications for recruitment through GATE 2018 will start after the admit card comes in ie. after January 5, 2018. Check this article. It gives all details and can be a helpful aid - https://engineering.careers360.com/articles/psu-recruitment-through-gate