Taking over gangs, turn informer (10)
I believe the answer is:
possessing
'taking' is the definition.
The definition and answer can be both to do with ownership as well as being present participle verbs.
Perhaps there's an association between them I don't understand?
'gangs turn informer' is the wordplay.
'gangs' becomes 'posses' (I can't justify this - if you can you should give a lot more credence to this answer).
'turn informer' becomes 'sing' (I've seen this before).
'posses'+'sing'='POSSESSING'
'over' is the link.
Can you help me to learn more?
(Other definitions for possessing that I've seen before include "Owning" , "Taking control of" .)