Adenovirus E1B protein usually refers to one of two proteins transcribed 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].
1. Yue Liu, April L. Colosimo, Xiang-Jiao Yang, and Daiqing Liao (2000). "Adenovirus E1B 55-Kilodalton Oncoprotein Inhibits p53 Acetylation by PCAF". Molecular and Cellular Biology: Vol 20: p5540-5553.