Company imports breathable gas for city (5)
I believe the answer is:
cairo
'for city' is the definition.
(Cairo is an example)
'company imports breathable gas' is the wordplay.
'company' becomes 'co' (abbreviation).
'imports' means one lot of letters goes inside another.
'breathable gas' becomes 'air' (we breathe air).
'co' placed around 'air' is 'CAIRO'.
(Other definitions for cairo that I've seen before include "Egyptian capital" , "North African capital" , "Capital of Egypt" , "Capital city on the Nile" , "Port upstream from the Nile delta" .)