A functional map of the nopaline synthase promoter.

This paper describes the first functional map of a promoter expressed from the plant chromosome. We have constructed a series of overlapping deletion mutants within the region upstream of the Ti-plasmid encoded nopaline synthase (nos) gene. By monitoring nos expression in tumour tissue we have inferred a functional map of the nos promoter. The maximum length of sequence upstream of the transcription initiation point required to express wild type levels of nopaline synthase is 88 bp. Within this region, the "CAAT" box is essential for maximal activity; deletion of this sequence reduced apparent nos expression by over 80%. Presence of an intact or partial "TATA" box in the absence of the "CAAT" box supports a barely detectable level of nopaline synthase. Removal of all sequences upstream of the nos coding sequence results in no detectable activity.