Article on yours truly’s subject matter (5)
I believe the answer is:
theme
'subject matter' is the definition.
(theme is a kind of subject matter)
'article on yours truly's' is the wordplay.
'article' becomes 'the' (the 'definite article' part of speech).
'on' is a charade indicator (letters next to each other).
'yours truly' becomes 'me'.
'the'+'me'='THEME'
(Other definitions for theme that I've seen before include "A subject or repeated melody" , "Unifying motif" , "basis for variations" , "Burden" , "Subject of a talk or piece of writing" .)