Stereospecific relationships between elements in an SV40/Adenovirus-2 heterologous promoter

Spacing mutations have been constructed between an SV40 72 bp enhancer element and the Adenovirus-2 major late promoter upstream element (Ad2MLP-UE), the Ad2MLP-UE and the Ad2MLP TATA-box and the SV40 72 bp enhancer and the TATA-box in the absence of the Ad2MLP-UE. A clear periodic pattern of transcription from the Ad2MLP was obtained by inserting multiples of half of a DNA turn between the SV40 enhancer and the Ad2MLP-UE. We interpret this as a stereospecific requirement for the spatial alignment between the enhancer element and either the Ad2MLP-UE or the TATA-box. Insertions between the upstream element and the TATA-box did not give a periodic transcription pattern, though insertion of half of a DNA turn increased the steady-state level of specific RNA. Unexpectedly, spacing mutations between the enhancer and TATA-box in which the upstream element had been point mutated gave indications of stereospecificity, whereas the same insertions with a deleted upstream element showed little requirement for a precise stereoalignment.