が・の（主語）

Inside a sentence that modifies a noun, the 「が」 that marks the subject can be replaced by 「の」: 「私が読んだ本」 = 「私の読んだ本」, 「背が高い人」 = 「背の高い人」. 「の」 makes it tighter, and Japanese people use it a lot in speech and writing.

•You can only swap inside a noun-modifying clause. In a main clause you cannot: 「雨が降る」 never becomes 「雨の降る」.

•When the subject is far from the noun it modifies, 「の」 can be misread as 'whose …', so keep 「が」: 「田中さんが日本語を教える学校」; 「田中さんの日本語を教える学校」 would be understood as 'Tanaka's Japanese'.