UASt regulates expression of SP with GFP(V63A.S65T) inserted between the N-terminal 10 amino-acid residues (SPn) and the C-terminal 26 amino acids (SPc). The 19aa signal sequence of SP is present at the N-terminus (so that the product is secreted) and 5-7 amino-acid-long spacers are placed between the GFP(V63A.S65T) and SP fragments.