[3] In 1981, Busslinger joined the lab of Richard A. Flavell at the MRC Institute Mill Hill in London as a postdoctoral fellow.
[5] In 1987, Max Birnstiel recruited Busslinger to join the newly founded Research Institute of Molecular Pathology (IMP) in Vienna, Austria, as one of the first Senior Scientists.
Protein purification and sequencing identified the B-cell-specific transcription factor as Pax5,[7] and gene inactivation in the mouse defined Pax5 an essential regulator of B cell development.
[10] In addition to Pax5, the Busslinger group investigated the role of other important transcription factors, such as E2A,[11] EBF1,[12] Ikaros, and Blimp1, in regulating distinct aspects of B cell development and immunity.
Busslinger also contributed to the current knowledge of how the large locus encoding the immunoglobulin heavy chain (IgH) protein undergoes spatial contraction by looping in early B cell development.