Chemical cross-linking coupled to mass spectrometry was used to study binary and ternary complexes involving cyclin-dependent kinase 19 (CDK19), cyclin-C, and an N-terminal fragment of subunit 12 of the Mediator complex (MED12 1-100). Cross-linking was performed using disuccinimidyl suberate (DSS). These results were generated in the context of the study published as Klatt et al., A precisely positioned MED12 activation helix stimulates CDK8 kinase activity, Proc. Natl. Acad. Sci. USA 2020 (DOI: 10.1073/pnas.1917635117) with the associated data set PXD015394, but were not included in the article.