Binds to the LIM domain of a wide variety of LIM domain-containing transcription factors. Acts as a coactivator together with otx2 to stimulate lhx1/lim1-mediated activation of the gsc promoter in the Spemann organizer. Acts synergistically with lhx1/lim1 and ssbp in axis formation. Forms homodimers and heterodimers. Interacts with the LIM domain of LIM/homeobox factor lhx1/lim1, and with lhx3/lim3 and lhx5/lim5. Activates lhx1/lim1 by binding. The stoichiometry of lhx1/lim1 and ldb1 is important for their function and an excess of ldb1 can inhibit lhx1/lim1 function. When bound to lhx1/lim1, escapes degradation by rnf12. The N-terminus interacts with the N-terminal region of rnf12. Ubiquitously expressed in the early gastrula before localizing to the dorsal region of the vegetal hemisphere, which contains the Spemann organizer. Expressed in the CNS, pronephros and tail bud in neurula and tail-bud stage embryos. Expressed in multiple adult tissues including brain, heart, lung, stomach, intestine, liver, spleen, kidney, ovary, muscle and skin. Expressed both maternally and zygotically during embryogenesis. The dimerization domain is located in the N-terminus. Undergoes rnf12-mediated ubiquitin-proteasome-dependent degradation. Lacks LIM-binding domain. Belongs to the LDB family.