Supplementary information to *Co-translational binding of importins to nascent proteins*

Various cellular quality control mechanisms support proteostasis. While, ribosome-associated chaperones prevent misfolding of nascent chains during translation, importins were shown to prevent the aggregation of specific cargoes in a post-translational mechanism prior to the import into the nucleoplasm. Here, we hypothesize that importins may already bind ribosome-associated cargo in a co-translational manner. We systematically measure the nascent chain association of all importins in Saccharomyces cerevisiae by selective ribosome profiling. We identify a subset of importins that bind to a wide range of nascent, often uncharacterized cargoes. This includes ribosomal proteins, chromatin remodelers and RNA binding proteins that are aggregation prone in the cytosol. We show that importins act consecutively with other ribosome-associated chaperones. Thus, the nuclear import system is directly intertwined with nascent chain folding and chaperoning. Files contain Python and MatLab scripts to analyze the data. Additionally, we deposit selective ribosome profiles for all importin SeRP experiments for all genes in S. cerevisiae. Furthermore, we provide AlphaFold models of Srp1 bound to identified NLS peptides.M.B. acknowledges funding by the Max Planck Society and the European Research Council (724349-ComplexAssembly)