Morphological transformation of human adenoviruses is determined to a large extent by gene products of region E1a.

The role of region E1a and E1b of human adenovirus (Ad) types 5 and 12 in determining the morphology of transformed colonies has been studied. Primary baby rat kidney cells were transfected with a mixture of plasmids containing Ad5 region E1a and Ad12 region E1b, or vice versa, and the morphology of the resulting transformed colonies was studied. It was found that the morphology of the colonies was correlated with the identity of the E1a region present in the cells; i.e., colonies transformed by Ad5 E1a plus Ad12 E1b resembled Ad5-transformed colonies, whereas those transformed by Ad12 E1a plus Ad5E1b resembled Ad12-transformed colonies. This suggested that the morphology of Ad-transformed cells is determined mainly by region E1a. To exclude the possibility that this phenomenon is due to an E1a-mediated and serotype-specific regulation of E1b expression and that the transformed phenotype is largely determined by region E1b, the experiments were repeated with Ad5 E1b plasmids in which the transcription regulation sequences had been replaced by the SV40 early promoter segment. In these plasmids E1b expression has become independent of region E1a. Foci of cells transformed by these E1b-SV40 promoter plasmids in the presence of either E1a of Ad5 or E1a of Ad12 again showed the same phenomenon, i.e., an Ad5-specific morphology with Ad5 E1a and Ad12-specific morphology with Ad12 E1a. Preliminary evidence showing that region E1b may regulate the concentration of E1a transcripts is discussed.