UAS regulatory sequences drive expression of Syt1, which is tagged at the C-terminal end with a Tag:CALI(4C) tag.
Vesicles at synapses in which Syt1Scer\UAS.T:Zzzz\4C (under the control of Scer\GAL4elav.PLu) is specifically photoactivated in the endocytic phase of the vesicle cycle are significantly larger than controls. Dramatically enlarged vesicular structures that often exceed 100nm are observed throughout the vesicle pool.
The T:Zzzz\4C tag binds the fluorescein derivative 4',5'-bis(1,3,2-dithioarsolan-2-yl)fluorescein (FlAsH). The T:Zzzz\4C tag can be used to visualise the localisation of the sytScer\UAS.T:Zzzz\4C protein after labelling with the FlAsH ligand. The binding of the FlAsH ligand to the T:Zzzz\4C tag also allows the sytScer\UAS.T:Zzzz\4C protein to be photoinactivated in vivo using the "fluorophore-assisted light inactivation" (FALI) technique, by illumination at 488nm. The inactivation of the protein is proportional to the duration of illumination, follows first-order kinetics and is specific (it does not impair syt-independent vesicle fusion).