Truncated green fluorescent protein mutants and their expression in Aplysia neurons.

We determined in detail the primary structure requirements for green fluorescence of the jellyfish green fluorescent protein (GFP) and of its improved mutants (S65T and 1167T). We performed a deletion mapping in combination with fluorescence-activated cell sorting (FACS) and spectrofluorometry. This showed that deletion of up to nine amino acids at the C-terminal end of GFP had no deleterious effect on the fluorescent activity of GFP; in fact the deletion increased intensity of fluorescence. Further truncation of up to 11 amino acids resulted in partial impairment in maximal fluorescence. The GFP fluorescence was completely disrupted when more than 12 amino acids were deleted out of the C-terminal. Truncated mutants or their fusion genes with lacZ emitted fluorescence when plasmids encoding them were introduced by microinjection into Aplysia neurons.