Intra- and inter-chromosomal interactions. (a) The β-globin gene, located approximately 50 kb downstream of the locus control region (LCR), is activated during erythropoiesis. The β-globin gene interaction with the LCR ensures high and efficient β-globin transcription, with the intervening sequence looping out. (b) Naïve T cells show a trans association between the TH2 LCR, on chromosome 11, and the IFN-γ promoter, on chromosome 10. This interaction is lost in favor of specific intra-chromosomal interactions following differentiation into TH1 or TH2 effector cells.