FIG. 7.
The HU-dependent cell cycle delay is sensitive to changes in the relative doses of dCBP and mei-41. (A) Eye discs heterozygous for mei-41RT are sensitive to HU treatment and arrest in S phase, while dCBP3/mei-41RT transheterozygotes have a significant increase in mitotic cells following HU treatment. Student's t tests determined the differences among the means. An asterisk indicates a significant difference (P < 0.01). Two different experiments from two separate matings gave the same qualitative result. (B) A duplication for dCBP (Tr31) restores the replication checkpoint in the dCBP3/mei-41RT transheterozygotes to wild-type levels. These are pooled results from three experiments (P < 0.001). (C) The genetic interactions suggest that dCBP and Mei-41 might interact directly. Coimmunoprecipitations show that dCBP and Mei-41 can be found together in complexes in Kc cells. The top panel is a Western analysis of mock-treated Kc cells that have been left untreated or treated with HU, Kc cells treated with siRNAs against dCBP, and Kc cells treated with siRNAs against mei-41. Gsα was used as an internal control for loading and protein transfer. The samples are 1/10 input of the extracts used for the immunoprecipitations. Results of dCBP immunoprecipitations (IP) from the extracts used in Western blotting are shown in the bottom panel. Although at low levels, Mei-41 is detected in the dCBP immunocomplexes from the control Kc cells but not in the dCBP immunoprecipitates from cells depleted of either dCBP or Mei-41. The 250-kDa marker (lane 1) cross-reacts with the fluorescent-labeled secondary antibodies used in the analysis of the immunoprecipitations.