The intergenic region of maize streak virus contains promoter elements involved in rightward transcription of the viral genome.

Maize streak virus (MSV), a geminivirus with a one-component genome, encodes a major coat protein RNA which accumulates in infected plants. Using a maize protoplast cell transient expression system, we have defined and studied the promoter which drives rightward transcription of the RNA encoding the coat protein. We have identified a 122 bp upstream segment that enhances promoter activity and functions as an upstream activating sequence (UAS). The UAS lies in the starting intergenic region of the viral genome and includes a region which is similar in all geminiviruses. The 122 bp UAS activates the MSV core promoter in an orientation, but not position, independent fashion. The MSV promoter UAS is interchangeable with a similar element in the cauliflower mosaic virus (CaMV) 35S RNA core promoter, that is the MSV UAS will activate the CaMV 35S core promoter and vice versa. However, the MSV promoter UAS specifically binds proteins in maize nuclear extracts which appear to differ from those bound by the functionally equivalent region of the CaMV 35S promoter.