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 (By similarity). Forms homodimers and heterodimers. Interacts with and activates lhx1/lim1. 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. Interacts with the N-terminal region of rnf12 (By similarity). The dimerization domain is located in the N-terminus. Undergoes rnf12-mediated ubiquitin-proteasome-dependent degradation. Belongs to the LDB family.