Update information. To understand the gain-of-toxicity of unprocessed prelamin A, we sought to identify the specific binding proteins of prelamin A that do not interact with mature lamin A. Because prelamin A is specifically localized to the nuclear envelope, we used ascorbate peroxidase 2 (APEX2)-based proximity labelling combined with mass spectrometry, which allows for temporally and spatially resolved proteomic mapping, to isolate the specific binding proteins of prelamin A.