p130 is related both in structure and function to the retinoblastoma tumor suppressor protein and p107 (collectively known as pocket proteins) and is known to regulate the activity of E2F transcription factors. E2F transcription factors regulate the expression of a number of genes important in cell proliferation, particularly those involved in the progression through G1 and into the S phase of the cell cycle. Binding of p130 converts E2F transcription factors from transcriptional activators