Cell Cycle-Regulated Transcription Factors; Bandshift Assays

Abstract

Transcriptional control plays an important role in the regulation of cell cycle progression in eukaryotes. Studies in yeast have shown that a family of transcription factors which controls the expression of several cell cycle regulated genes, in particular genes involved in DNA synthesis, tightly regulates the commitment of a cell to enter into S phase (reviewed by Andrews and Mason 1993). Although in higher eukaryotes, similar control mechanisms are just beginning to be discovered and understood, several cell cycle-regulated transcription factors have been already described. This chapter presents as an example the bandshift analysis of the transcription factor E2F, which appears to be centrally involved in control of the G1/S transition in mammalian cells (Nevins 1992) and may serve as a paradigm for cell cycle regulated transcription factors. Indeed it has been shown that:

• Expression of E2F in quiescent cells induces S phase entry.

• Different forms of E2F are present at various stages of the cell cycle (Mudryj et al. 1991; Pagano et al. 1992a).

• E2F associates physically to several proteins of proven capacity as regulators of the cell cycle, like Cyclins, Cdks, the product of the retinoblastoma gene, p107, p130, etc. (Lees et al. 1992; Cobrinik et al. 1993; Schwarz et al. 1993).

• E2F is a target for several viral oncogenes that are known to override growth control mechanisms acting at the G1/S boundary (Phelps et al. 1991).