DNA fragments from promoter regions of the geminivirus, African cassava mosaic virus, were cloned into pG1, a vector based on pUC18, producing transcriptional fusions with the β-glucuronidase (GUS) gene and nopaline synthase termination sequence. The activity of each promoter construct was assessed by analysing the transient expression of GUS in protoplasts. The results demonstrated that constructs containing the common region of DNA A showed much stronger promoter activity in the complementary sense than in the viral sense. These results were supported by the analysis of promoter activity in transgenic plants. In comparison, in protoplasts a region upstream of the AC2 open reading frame was shown to have moderate promoter activity. Unlike DNA A, the complementary sense DNA B promoter constructs had weak activity; the viral sense DNA B promoter constructs appeared to be regulated by host factors. The implications of these results for the regulation of early and late genes are discussed.


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