Urban lecture is a subject of conversation (4,2,3,4)
I believe the answer is:
talk of the town
'urban lecture' is the definition.
The definition and answer can be both related to communication as well as being singular nouns.
Perhaps you can see a link between them that I can't see?
'subject of conversation' is the wordplay.
I cannot quite see how this works, but
'of' could be 'o' and 'o' is found in the answer.
'conversation' could be 'talk' (talk is a kind of conversation) and 'talk' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
'is a' acts as a link.
Can you help me to learn more?
(Other definitions for talk of the town that I've seen before include "What everyone's gossiping about" , "(Subject of) local gossip" .)