Figure 1

Schematic diagram of our hypothesis. Filled rectangles indicate cis-elements in promoters. Circles indicate transcription factors, and transcription factor x' binds to cis-element x. Cis-element 2 is common in both miRNA and target gene promoters, while cis-elements 1 and 3 are specific in target and miRNA genes, respectively. In this figure, all transcription factors are regarded as activators. (A) In a case that transcription factor 1' binds to cis-element 1, only the target gene is transcribed. (B) In a case that transcription factor 2' binds to cis-element 2, both the miRNA and the target genes are transcribed. The miRNA subsequently downregulates the expression of the target gene after several transportation and processing steps. In a case that transcription factor 3' binds to cis-element 3, the expression of genes whose promoters contain cis-element 3 will be downregulated by the miRNA.