E2F transcription factors play an important role in the regulation of cell cycle progression. E2F6, the most recently identified member of the E2F family, is a retinoblastoma-protein-independent transcriptional repressor that is required for developmental patterning of the axial skeleton. It has recently been shown that theE2f6locus produces two different mRNAs, E2F6 and E2F6b. The E2F6b mRNA contains an additional exon that is inserted by alternative splicing.