Figure 1.

Specific colocalization of genes on the same and different chromosomes, as detected using a combination of fluorescent in situ hybridization (FISH) and 3C technology. (a,b) A representation of part of a mouse erythroid-cell nucleus, showing the edge of the territory of one chromosome and two active genes Hbb-b1 and Eraf looping out from the territory. (a) Osborne et al. [4] found that colocalization within the nucleus of these two genes, together with other active genes (not shown) distributed over the same 40 Mbp region of the chromosome, appears to be driven at least in part through the shared colocalization with the same focal concentration of RNA polymerase II (Pol II), in a 'transcription factory' (circles). (b) When the genes are not localized to Pol II foci, for example, when Eraf is inactive (black), they are not colocalized. (c) Association in naive mouse CD4⁺ T cells between the gene encoding the cytokine interferon γ (IFNγ) and specific sequences in the T_H2 locus, including the genes encoding interleukin 5 (IL5) and the DNA-repair protein Rad50 as well as a DNase I hypersensitive site called RHS6 [5]. In this cell type, both gene loci are poised for rapid induction of low levels of expression. CNS1 and CNS2 indicate conserved noncoding sequences near the IFNγ gene on chromosome 10. The genes may be associated with a shared nuclear body represented by the oval, for instance a 'transcription factory', but this has not been demonstrated [5].