Figure 3. Secondary structure of the promoter of an rDNA operon. (A) A-box and B-Box (blue) are interacting highly conserved for all metazoan animals. The pRNA itself (red) of all here reported sequences can fold into two possible secondary structures (B and C). The first hairpin (green box) and half of the second hairpin (red box) are part of the UCE (-180/-156–-107 nt). Color boxes represent interacting regions of pRNAs colored identical in (B and C). Promoter-associated RNAs may fold into one of the structures depending on their interaction to NoRC.