Informed (of) (5)
'informed of' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for aware that I've seen before include "well informed" , "Conscious, sentient" , "Having knowledge of, informed" , "Alert, conscious of" , "Acquainted with or mindful of" .)
(Other definitions for upon that I've seen before include "Straddling" , "voucher, business stopped" , "Onto" , "Carried - on top" , "Children's tales may begin ` `Once .... a time' '" .)