RNAi Double-stranded RNAs (dsRNAs) were made using gld-2 cDNAs (pJK830, exons 2-8 or pJK831, exons 16-18) as templates. Young adults were either injected with 2 mg ml 21 gld-2 dsRNA or soaked in 10 ml of 2 mg ml 21 gld-2 dsRNA for 12 h at 20 8C or mock-treated by injection with M9 buffer. Embryos were collected at defined intervals after treatment and processed together. Poly(A) polymerase assayProteins were in vitro translated using the TNT coupled transcription-translation system (Promega), and assayed using buffer conditions essentially as described 26 . For scintillation counting, poly(A) (Roche) was used as substrate. For gel assays, we used RNA oligo, C 35 A 10 (Dharmacon), a 45-nucleotide and supplemental 1 mM MgCl 2 . Products were analysed on 12% sequencing gels.

The Forkhead transcription factors AFX, FKHR and FKHR-L1 are orthologues of DAF-16, a Forkhead factor that regulates longevity in Caenorhabditis elegans. Here we show that overexpression of these Forkhead transcription factors causes growth suppression in a variety of cell lines, including a Ras-transformed cell line and a cell line lacking the tumour suppressor PTEN. Expression of AFX blocks cell-cycle progression at phase G1, independent of functional retinoblastoma protein (pRb) but dependent on the cell-cycle inhibitor p27kip1. Indeed, AFX transcriptionally activates p27kip1, resulting in increased protein levels. We conclude that AFX-like proteins are involved in cell-cycle regulation and that inactivation of these proteins is an important step in oncogenic transformation.

Abnormal chromosome content - also known as aneuploidy - is the most common characteristic of human solid tumours. It has therefore been proposed that aneuploidy contributes to, or even drives, tumour development. The mitotic checkpoint guards against chromosome mis-segregation by delaying cell-cycle progression through mitosis until all chromosomes have successfully made spindle-microtubule attachments. Defects in the mitotic checkpoint generate aneuploidy and might facilitate tumorigenesis, but more severe disabling of checkpoint signalling is a possible anticancer strategy.