English dons translated Proust for companies (7)
I believe the answer is:
troupes
'for companies' is the definition.
('troupe' can be a synonym of 'company')
'english dons translated proust' is the wordplay.
'english' becomes 'E' (abbreviation as in OED).
'dons' means one lot of letters goes inside another (don can mean to wear or be covered in).
'translated' indicates anagramming the letters.
'proust' anagrammed gives 'troups'.
'e' inserted within 'troups' is 'TROUPES'.
(Other definitions for troupes that I've seen before include "performers of Swan Lake" , "Groups of entertainers" , "The acrobatic ones" .)