LIM domain binding protein 1 (LDB1) is a transcriptional regulator that plays a key role in regulating the function of LIM homeodomain (LHX) and nuclear LIM-only (LMO) transcription factors, with additional roles in Wnt signalling. Mouse knockouts of Ldb1 are embryonic lethal, with mice displaying a pleiotropic phenotype encompassing a range of developmental defects. The dimerization domain of LDB1 is essential for chromatin looping at the β globin locus, and has been used in the construction of artificial looping factors that trigger gene activation in erythroid cells. LDB2, a close homolog of LDB1, has no detectable phenotype. Rather it appears to be expressed when high levels of LDB1 activity are required. We’ve been exploring how these proteins multimerize through their dimerization domains. LDB1 and LDB2 don’t appear to form hybrid complexes in vitro, but although the structures of the proteins are essentially identical, LDB2 preferentially forms tetramers rather than dimers, supporting its role in promotion self-association. Mutation of the bipartite dimerization interfaces of LDB1 is tricky, as many mutants that disrupt dimerisation lead to insoluble or unstable protein. However, it has been possible to engineer variants of LDB1 that preferentially homo- or heterodimerise, and have reduced capacity to interact with wild-type LDB1, which hold some promise for modulating the activation of other genes.