Mark's new director in authority (7)
I believe the answer is:
command
'authority' is the definition.
(I know that command is a type of authority)
'mark's new director' is the wordplay.
'mark' becomes 'comma' (punctuation mark).
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'director' becomes 'd' (abbreviation eg in film reviews).
'comma'+'n'+'d'='COMMAND'
'in' is the link.
(Other definitions for command that I've seen before include "Instruction, order" , "Direct" , "Bid" , "Understanding" , "Authoritative instruction" .)