E2F3a

E2F3a is a transcription factor belonging to the E2F family. These proteins play a crucial role in regulating the cell cycle, particularly in the transition from the G1 phase to the S phase, which is essential for DNA replication. E2F3a is one of two isoforms transcribed from the E2F3 gene, the other being E2F3b. The distinction between these isoforms arises from alternative splicing. E2F3a is characterized by its ability to bind to specific DNA sequences, known as E2F sites, within the promoter regions of target genes. Upon binding, it can activate or repress gene expression, thereby influencing the synthesis of proteins required for cell division.

The activity of E2F3a is tightly regulated by the retinoblastoma protein (Rb) and its family members. In quiescent or G1-arrested cells, Rb proteins bind to E2F3a, forming an inhibitory complex that prevents E2F3a from activating transcription. As cells enter the S phase, cyclin-dependent kinases (CDKs) phosphorylate Rb, leading to its dissociation from E2F3a. Once released, E2F3a can then bind to its target promoters and drive the expression of genes involved in DNA synthesis, such as those encoding DNA polymerases and thymidine kinase. Dysregulation of E2F3a activity has been implicated in various cancers, where its uncontrolled activation can promote unrestrained cell proliferation.