A prepositional phrase beginning with "of" that represents where a person works or where he is from and that follows a proper noun takes commas around it. Other prepositional phrases do not take these commas.
...John Jones, of Smith and Jones...
...John Jones, of Buffalo...
...Mary Smith, of USC, is speaking at the symposium.
...Mary Smith, of Seattle, Washington, is visiting next week.
Happy punctuating!
Margie