Eight copies of the lexAop regulatory sequence drive expression of the Syt1 coding sequence which is tagged at the C-terminal end with a non-fluorescent 'spaghetti monster GFP' ('smGdP') marker which consists of 10 copies of the Tag:OLLAS epitope inserted in groups into the backbone of a superfolder green fluorescent protein which has been rendered non-fluorescent by mutation. The smGdP marker has been optimised for Drosophila codon usage.