The specificity of humoral immune responses depends on the functional rearrangement and expression of only one allele of immunoglobulin (Ig) genes. Here, we analyzed the comprehensive proteome of the murine Ig Emu enhancer, which governs the rearrangement and expression of the Ig mu heavy chain allele. By mass spectrometry of proteins bound at wild type versus mutant Emu enhancers, we identified Emu-binding proteins and associated multi-protein complexes. We found that the MSL/MOF complex, a regulator of gene dosage compensation in flies, binds Emu via transcription factor YY1 and facilitates Emu-driven chromatin looping and promoter interaction. Msl2 gene knockout in primary pre-B cells or Mof heterozygosity in mice reduced mu gene expression. In this data set we compare proteins binding to the wild-type Emu versus a DNA bait control for which the E1 box of the core enhancer region was mutated (E1mt).The E1mt abrogates binding of proteins recognizing the E1 box (e.g. YY1). Max LFQ quantitative proteomics was employed in an approach incubating wild-type and control DNA with (unlabeled) nuclear extracts.