Stage actors alert, the sleep ends (4)
I believe the answer is:
step
'stage' is the definition.
(thesaurus)
'actors alert the sleep ends' is the wordplay.
'ends' suggests the final letters.
The last letters of 'actors alert the sleep' are 'STEP'.
(Other definitions for step that I've seen before include "Gradation" , "Set foot down on pest" , "Rung, dance movement" , "Foot movement" , "Pace; foothold" .)