THE TRANSCRIPTION FACTOR E2F IS REQUIRED FOR S-PHASE DURING DROSOPHILA EMBRYOGENESIS

Overexpression of the E2F-1 cDNA in mammalian cells disrupts normal co ntrol of the cell cycle and drives cells into S phase. Whereas elimina ting E2F activity would test its inferred involvement in the G(1)-S tr ansition, elimination is complicated by the existence of gene families encoding mammalian E2F. Here we identify mutations in a single essent ial Drosophila gene, dE2F, that encodes a homolog of the mammalian E2F gene family. Embryos homozygous for null mutations of dE2F complete e arly cell cycles, presumably using maternal contributions of gene prod ucts, but DNA synthesis falls to virtually undetectable levels in cycl e 17. Mutant embryos also lack the pulses of coordinate transcription of genes encoding replication functions that usually accompany each tr ansition from quiescence to S phase. We conclude that in most cells dE 2F is essential for a G(1)-S transcriptional program and for G(1)-S pr ogression.