Expression of adenovirus type 5 E4 Orf2 protein during lytic infection.

The human adenovirus type 5 E4 transcription unit has the potential to encode at least seven distinct polypeptides from reading frames accessed by differential splicing of a single primary transcript. Only some of these polypeptides have yet been detected during viral infection of cultured cells. Mutational inactivation of the reading frames whose products have not been described has no apparent effect on the growth of virus in standard cultured human cell lines, indicating that these proteins, if they exist, have only a subtle, non-essential role in the replication cycle. We have raised an antiserum to one of these undefined products, E4 Orf2, expressed in bacteria. Using this reagent, it was possible to show that Orf2 was expressed during the lytic cycle in HeLa cells, being a soluble cytoplasmic component appearing with early kinetics. No association of Orf2 protein with other infected cell components was detected.