Mutations of the Drosophila dDP, dE2F, and cyclin E genes reveal distinct roles for the E2F-DP transcription factor and cyclin E during the G1-S transition.
Activation of heterodimeric E2F-DP transcription factors can drive the G1-S transition. Mutation of the Drosophila melanogaster dE2F gene eliminates transcriptional activation of several replication factors at the G1-S transition and compromises DNA replication. Here we describe a mutation in the Drosophila dDP gene. As expected for a defect in the dE2F partner, this mutation blocks G1-S transcription of DmRNR2 and cyclin E as previously described for mutations of dE2F. Mutation of dDP also causes an incomplete block of DNA replication. When S phase is compromised by reducing the activity of dE2F-dDP by either a dE2F or dDP mutation, the first phenotype detected is a reduction in the intensity of BrdU incorporation and a prolongation of the labeling. Notably, in many cells, there was no detected delay in entry into this compromised S phase. In contrast, when cyclin E function was reduced by a hypomorphic allele combination, BrdU incorporation was robust but the timing of S-phase entry was delayed. We suggest that dE2F-dDP contributes to the expression of two classes of gene products: replication factors, whose abundance has a graded effect on replication, and cyclin E, which triggers an all-or-nothing transition from G1 to S phase.
Duronio
R J
RJ
Department of Biology, Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill 27599, USA. duronio@med.unc.edu
Bonnette
P C
PC
O'Farrell
P H
PH
D000595:Amino Acid Sequence; D000818:Animals; D002352:Carrier Proteins; D002453:Cell Cycle / Q000235:genetics*; D018797:Cell Cycle Proteins; D019927:Cyclin E / Q000235:genetics*; D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D004331:Drosophila melanogaster / Q000166:cytology / Q000235:genetics*; D050684:E2F Transcription Factors; D016193:G1 Phase; D017344:Genes, Insect; D008969:Molecular Sequence Data; D009154:Mutation; D011506:Proteins / Q000235:genetics*; D056465:Retinoblastoma-Binding Protein 1; D016196:S Phase; D015534:Trans-Activators; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism
D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D019927:Cyclin E; D004268:DNA-Binding Proteins; C088053:Dp transcription factor, Drosophila; D029721:Drosophila Proteins; D050684:E2F Transcription Factors; D011506:Proteins; D056465:Retinoblastoma-Binding Protein 1; D015534:Trans-Activators; D014157:Transcription Factors