Late in infection, transcription of the EIIa gene is initiated primarily at map unit 72 of the adenovirus genome. A cell-free nuclear extract system was used to determine sequence elements important for the function of this late promoter. In such a system, the transcriptional activity of a circular template was found to be much higher (5- to 10-fold) than that of a linear template. The effect of template topology appeared to be dependent on two distal upstream elements with 5' boundaries located near -265 to -223 and -147 to -133 (in relation to the initiation site), since deletions of these regions reduced transcription of the circular template, in a stepwise fashion, to a level similar to that observed with the linear template. Further deletions revealed an element in the -116 region that appeared to be more important for transcription of the circular template (10-fold reduction) than for transcription of the linear template (3-fold reduction). Lastly, deletion of the TACAAA sequence in the -29 region resulted in further reduction in transcription, indicating that this element functions as a promoter in vitro.