The hepatitis B virus S promoter comprises A CCAAT motif and two initiation regions.

The hepatitis B virus S (major surface gene) promoter is embedded in two overlapping open reading frames and specifies several transcripts with heterogeneous 5' termini. We have identified the cis-elements necessary for S promoter function. A single upstream CCAAT element is essential for high level expression in both liver and non-liver cells. No TATA box is present, but two regions surrounding the initiation sites can function separately as initiating elements. These results show that the S promoter has a simple requirement for upstream activating sequences, but a complex initiation region. Therefore, it may provide a suitable model system for studying transcription initiation in non-TATA type promoters.