Adenovirus E1B protein usually refers to one of two proteins transcribed

Transcription (genetics)

Transcription is the process of creating a complementary RNA copy of a sequence of DNA. Both RNA and DNA are nucleic acids, which use base pairs of nucleotides as a complementary language that can be converted back and forth from DNA to RNA by the action of the correct enzymes...

 from the E1B gene of the adenovirus: a 55kDa protein and a 19kDa protein. Primarily, the two work to delay cell lysis during viral replication. Afterwards, they help induce cell death and control the export of viral transcripts. Specifically, the E1B 55kDa protein inhibits p53 acetylation, and therefor activation, by PCAF [1].