Hi, 

The filling up of 15% seats of government medical colleges of various states is conducted by MCC.

Same goes for the state of tamil nadu too. If you want to apply under all india quota counselling then you only need to register under mcc site and pay the concermed fee.

However for admission under 85% state quota counselling you would have to fill the forms released by the concerned counselling authority of tamil nadu.

All the best