Make public investment in company capital (5)
I believe the answer is:
cairo
'capital' is the definition.
(capital of Egypt)
'make public investment in company' is the wordplay.
'make public' becomes 'air' (I've seen this in another clue).
'investment in' means one lot of letters goes inside another.
'company' becomes 'co' (abbreviation).
'air' placed into 'co' is 'CAIRO'.
(Other definitions for cairo that I've seen before include "City near the Nile delta" , "African city" , "Al Qahira" , "Egypt's capital" , "North African capital" .)