Research article

Involvement of an SCF^Slmb complex in timely elimination of E2F upon initiation of DNA replication in Drosophila

Jean-Karim Hériché¹ , Dan Ang² , Ethan Bier² and Patrick H O'Farrell¹

¹Department of Biochemistry and Biophysics, University of California, San Francisco, 513 Parnassus Street, San Francisco, CA 94143-0448, USA

²Section of Cell and Developmental Biology, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0349, USA

author email corresponding author email

BMC Genetics 2003, 4:9doi:10.1186/1471-2156-4-9

Published:	4 June 2003

Abstract

Background

Cul1 is a core component of the evolutionarily conserved SCF-type ubiquitin ligases that target specific proteins for destruction. SCF action contributes to cell cycle progression but few of the key targets of its action have been identified.

Results

We found that expression of the mouse Cul1 (mCul1) in the larval wing disc has a dominant negative effect. It reduces, but does not eliminate, the function of SCF complexes, promotes accumulation of Cubitus interruptus (a target of SCF action), triggers apoptosis, and causes a small wing phenotype. A screen for mutations that dominantly modify this phenotype showed effective suppression upon reduction of E2F function, suggesting that compromised downregulation of E2F contributes to the phenotype. Partial inactivation of Cul1 delayed the abrupt loss of E2F immunofluorescence beyond its normal point of downregulation at the onset of S phase. Additional screens showed that mild reduction in function of the F-box encoding gene slimb enhanced the mCul1 overexpression phenotype. Cell cycle modulation of E2F levels is virtually absent in slimb mutant cells in which slimb function is severely reduced. This implicates Slimb, a known targeting subunit of SCF, in E2F downregulation. In addition, Slimb and E2F interacted in vitro in a phosphorylation-dependent manner.

Conclusion

We have used genetic and physical interactions to identify the G1/S transcription factor E2F as an SCF^Slmb target in Drosophila. These results argue that the SCF^Slmb ubiquitin ligase directs E2F destruction in S phase.