From a press release issued by FIM:

FIM announcement. Changes to the 2005 MotoGP calendar

Following the lack of a signed contract, the Rio Grand Prix is cancelled. The Portuguese Grand Prix will be moved to April 17. The Turkish Grand Prix will take place on the new circuit of Istanbul on October 23. The calendar is the following:

Grand Prix Circuit
4-10 Spain Jerez
4-17 Portugal Estoril
5-1 China Shanghai
5-15 France Le Mans
6-5 Italy Mugello
6-12 Catalunya Catalunya
6-25 Netherlands ** Assen
7-10 United States * Laguna Seca
7-24 Great Britain Donington Park
7-31 Germany Sachsenring
8-28 Czech Republic Brno
9-18 Japan Motegi
9-25 Malaysia Sepang
10-1 Qatar ** Doha
10-16 Australia Phillip Island
10-23 Turkey *** Istambul
11-6 Valencia Valencia

*: Only MotoGP class
**: Saturday
***: Subject to contract