Chromosome Conformation Capture (3C). (A) Linear depiction of a gene with promoter on the left, terminator on the right. (B) A transient gene loop formed by juxtaposition of the promoter and the terminator. (C) Schematic depiction of 3C methods to detect gene loops. The tandem primer pair in the linear structure (panel a) becomes a convergent primer pair following the 3C protocol. According to 3C, the abundance of the ligation product, as detected by PCR, is a measurement of the frequency with which two loci interact (Dekker et al., 2002; Dekker, 2006).