The Q system is an expression system similar in principle to the GAL4/UAS system but based on genes from the Neurospora crassa qa cluster.  It is composed of two regulatory proteins (QF and QS) and a binding site for QF called QUAS (QF upstream activating sequences). QF is a transcriptional regulator that binds to QUAS sequences and transcriptionally activates downstream genes.  QS is a QF repressor that effectively blocks QF-mediated transcriptional activation.  QS repression of QF can be suppressed by quinic acid.  QF-based MARCM can be used independently or in conjunction with GAL4-based MARCM to refine and expand the range of expression patterns available via GAL4-based expression alone.

Primary reference: Potter, C.J., Tasic, B., Russler, E.V., Liang, L., and Luo, L. 2010. The Q system: A repressible binary expression system for transgene expression, lineage tracing and mosaic analysis. Cell. 141(3):536-548.

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