A sequence cassette that encodes a GAL4::VP16 driver has been inserted into the second coding exon of pyr. A T2A self-cleaving peptide is present upstream of the driver sequence and stop codons in all three frames are present downstream of the driver sequence, to ensure that the driver is translated independently and not as part of a fusion protein with pyr. This results in the expression of a GAL4::VP16 driver under the control of the endogenous pyr regulatory sequences, including 5' and 3' UTR sequence, while the presence of the stop codons is expected to result in a null pyr allele.