Fig. 3. Regulated proteolysis generates a normal temporal distribution of ORC1 protein even upon constitutive ORC1 transcription. Expression of various proteins under control of the GMR promoter (A–C, E–H, K and L), which is active in all cells posterior to the MF (arrowhead) in the eye disc, or the engrailed (en) promoter (I and J), which is active in all cells of the posterior compartment of the wing disc. High magnification views of the area of the eye disc boxed in (A) reveal that cells with high levels of ORC1–GFP are CycB positive with no BrdU incorporation (not shown), and therefore in G₂ (B–D). FACS analysis reveals that ORC1–GFP is depleted in G₁ phase eye (G and H) and wing (I and J) imaginal disc cells, even if transcription of ORC1–GFP is driven constitutively. High magnification views of cells immediately posterior to the MF reveal co-localization of ORC1–GFP and CycB following nuclear envelope breakdown and the presence of late telophase cells with paired nuclei bearing high levels of ORC1–GFP but no significant CycB (K–M).