A long time ago, JR was government run. But now it has private management.
「JRは昔国鉄でした。今は民営です。」は英語で「Japan Railways (JR) used to be the Japanese National Railways (run by the government). But now it's under private management」という表現が良いと思います。
「A long time ago, JR was government run. But now it has private management.」という表現も言えます。