First-class journalist backed assistant (4)
I believe the answer is:
aide
'assistant' is the definition.
(aide is a kind of assistant)
'first-class journalist backed' is the wordplay.
'first class' becomes 'ai' (A1 - top quality).
'journalist' becomes 'ed' (short for editor).
'backed' says the letters should be written backwards.
'ed' in reverse letter order is 'de'.
'ai'+'de'='AIDE'
(Other definitions for aide that I've seen before include "One to assist" , "Assistant to a more senior person" , "a help" , "Political assistant" , "Idea (anag)" .)