The binding of nuclear factors to the as-1 element in the CaMV 35S promoter is affected by cytosine methylation in vitro.

Transcriptional gene silencing (TGS) is often associated with an increased level of cytosine methylation in the affected promoters. The effect of methylation of the cauliflower mosaic virus (CaMV) 35S promoter sequence on its binding to factors present in the nuclei was analyzed by electrophoretic mobility shift assays using extracts of petunia flowers. Specific DNA-protein interactions were detected in the region of the CaMV 35S promoter that contains the as-1 element and the region between - 345 and - 208. The binding of protein factor(s) to the as-1 element was influenced by cytosine methylation, whereas the binding to the region between - 345 and - 208 was unaffected. The results suggest that cytosine methylation of the as-1 element potentially affects the activity of the CaMV 35S promoter.