UASt regulatory sequences drive expression of a VHH(GFP4) nanobody-containing 'LARIAT' (Light-activated reversible inhibition by assembled trap) system. LARIAT is a two component system that can be used to reversibly inhibit protein function by sequestering target proteins into large, optically assembled protein complexes in vivo (for more details, see PMID:24793453). In this case, proteins tagged with GFP (or another related fluorescent tag that is bound by VHH(GFP4)) can be reversibly sequestered and inhibited. The two components are expressed as a single mRNA which gives rise to two distinct proteins due to the presence of a P2A peptide between the two coding sequence (this also ensures that both components are present in equal amounts). The first open reading frame in P{UAS-LARIAT.VHH(GFP)} (represented in FlyBase by Zzzz\VHH^{GFP4.UAS.LARIAT}) encodes the VHH(GFP4) nanobody tagged with SNAP-tag(Unk) and with CRY2(PHR). The second open reading frame in P{UAS-LARIAT.VHH(GFP)} (represented in FlyBase by Atha\CIB1^{CIBN(ΔNLS).UAS.LARIAT}) encodes the Tag:MP(AV) multimerization domain fused to CIBN(ΔNLS). When stimulated by blue light, the CRY2(PHR) portion of the Zzzz\VHH^{GFP4.UAS.LARIAT} component simultaneously oligomerizes and binds to the CIBN(ΔNLS) portion of the Atha\CIB1^{CIBN(ΔNLS).UAS.LARIAT} component. This results in large protein clusters, by promoting interconnection amongst the Atha\CIB1^{CIBN(ΔNLS).UAS.LARIAT} multimers, while the presence of the VHH(GFP4) nanobody in the Zzzz\VHH^{GFP4.UAS.LARIAT} component means that GFP-tagged proteins are sequestered and trapped in the protein cluster.