E1b

E1B, short for early region 1B, is a region of the genome of adenoviruses that encodes several proteins that modulate the host cell environment to promote viral replication. The two best characterized products are E1B-55K and E1B-19K, with additional smaller E1B-derived proteins described in some serotypes.

E1B-55K is a regulatory protein that, together with the viral E4orf6 protein, forms an E3 ubiquitin ligase complex that targets the cellular tumor suppressor p53 for ubiquitin-dependent degradation. This reduces p53-mediated cell cycle arrest and apoptosis, thereby facilitating viral replication. E1B-55K also participates in other aspects of viral gene expression and RNA processing essential for efficient viral replication.

E1B-19K is a member of the Bcl-2 protein family and localizes to mitochondria where it inhibits apoptotic signaling. By preventing activation of Bax and Bak and subsequent mitochondrial outer membrane permeabilization, E1B-19K helps infected cells survive longer to support virion production.

Some adenovirus serotypes express additional E1B-derived proteins, such as E1B-14.7K, which contribute to anti-apoptotic effects and the overall capacity of the virus to counteract host defenses. The E1B region functions in concert with other viral early genes, particularly E1A, to push the host cell into an environment conducive to viral DNA replication and production.

In medicine, E1B has attracted interest in the development of oncolytic adenoviruses. Deletions or disruptions of E1B-55K were explored to create tumors that selectively support viral replication, notably in p53-deficient cancers, though the determinants of selectivity are multifactorial and not solely defined by p53 status.