Answer:

Strangely enough I could find no better descriptions than: http://www.conncoll.edu/ccacad/zimmer/GFP-ww/history.html and http:/www.cryst.bbk.ac.uk/PPS2/projects/jonda/chromoph.htm

The chromophore.

I assume there has been a ring-closure between the C=O of Ser-65 and the backbone N of Tyr-66:

Two suggested mechanisms for the generation of the fluorophore.

Gly-67 might play a role in the production of the fluorophore, but comes out unharmed.