Neurospora crassa QA-1F (UniProtKB:P11638) is a transcriptional activator that contains both a sequence-specific DNA-binding domain and a transcriptional activation domain (reviewed in PMID:1825499). QA-1F binds specifically to the QUAS regulatory sequence. This property can be utilized to form a binary expression system to control the spatial and temporal expression of a gene of interest: a transgene or modified endogenous locus in which the target gene of interest is downstream of QUAS sequences is combined with a transgene or modified endogenous locus encoding a compatible 'QF driver'. The QF entry in FlyBase represents a driver corresponding to either the naturally occurring QA-1F protein, or where the precise variant is unknown/unspecified, but both DNA-binding domain and transcriptional activation domain are derived from QA-1F. The exact sequence of the driver may thus differ depending on the particular transgene or modified endogenous locus being used. The expression pattern of a gene of interest can be further refined by adding the QS suppressor, which binds to QF such that although it can still bind the QUAS sequence it can no longer activate transcription. The suppression of QF by QS can itself be suppressed by feeding flies with quinic acid, providing a further level of regulation (FBrf0210697, reviewed in FBrf0214230, FBrf0233764).