Record single up around number four in chart (5)
I believe the answer is:
enrol
'record' is the definition.
(I've seen this before)
'single up around number four in chart' is the wordplay.
'single' becomes 'lone' (synonyms).
'up' is a reversal indicator (in down clue: letters go upwards).
'around' is an insertion indicator.
'number four in chart' becomes 'r' (4th letter of 'chart').
'lone' back-to-front is 'enol'.
'enol' going around 'r' is 'ENROL'.
(Other definitions for enrol that I've seen before include "Add to list of members" , "Register (as student)" , "Recruit" , "Join as member" , "Join up, sing on" .)