Function of register to be announced (4)
I believe the answer is:
role
'function' is the definition.
('role' can be a synonym of 'function')
'register to be announced' is the wordplay.
'register' becomes 'roll' (list of names).
'to be announced' shows a homophone (sound like).
'roll' sounds like 'ROLE'.
'of' is the link.
(Other definitions for role that I've seen before include "Function in life" , "Duty" , "Impersonation" , "Actor's part" , "A part of lore" .)