The P{UAS-RB.cct} construct is a cell cycle reporter in which UAS sequences drive expression of a single mRNA that can give rise to two distinct fusion proteins, due to the presence of a self cleaving T2A element between the two open reading frames. The first protein is a blue fluorescent protein that is comprised of EBFP2 fused to a nuclear localization signal and to a degron sequence from the Cdt1 gene. The presence of the Cdt1 degron means that it is degraded specifically during S phase. The second protein is a red fluorescent protein comprised of tdTomato fused to a nuclear localization signal and to a degron sequence from the CycB gene (Tag:degron(CycB)). The presence of the CycB degron means that it is degraded specifically during late M and G1.