E1A

E1A refers to the early region 1A gene of adenoviruses, which encodes the main regulatory immediate-early proteins that set the stage for viral replication and reprogram host cell transcription. The E1A transcripts produce two major protein products, typically called the 12S and 13S E1A proteins, from alternative splicing. The 13S isoform is longer and contains an additional transcriptional activation domain known as CR3; both isoforms share conserved regions CR1 and CR2 that mediate protein interactions.

E1A proteins bind and inactivate the retinoblastoma (Rb) family pocket proteins (Rb, p107, p130), releasing E2F transcription factors and driving G1/S cell cycle progression. They also recruit transcriptional coactivators such as p300/CBP and other factors to activate transcription of viral early genes and many cellular genes, promoting a cellular environment compatible with viral replication.

In infected quiescent cells, E1A is essential for activating the viral genome and allowing replication of adenovirus. E1A often acts in cooperation with the E1B region (in particular E1B 55K) to transform cells in culture, but transformation is not universal and requires other factors.

Because of its central role in cell cycle control and transcription, E1A has been used as a research tool to study RB/E2F pathways and transcriptional regulation. E1A-based vectors have been used in basic research and in the development of virus-based therapies, including oncolytic adenoviruses, where modifications to E1A influence host range and tumor selectivity.