The family of AT-rich interactive domain (ARID) containing proteins -Arids- contains 15 members that have almost exclusively been described as DNA-binding proteins. Interestingly, a decade ago the family memberArid5awas found to bind and stabilize mRNAs of immune system key players and thereby account for driving inflammatory and autoimmune diseases. How exactly binding to DNA and RNA is coordinated by theArid5aARID domain remains unknown, mainly due to the lack of atom-resolved information on nucleic acid-binding. This in particular applies to the protein’s ARID domain, despite the comfortable size of its core unit for NMR-based investigations. Furthermore, the core domain of ARID domains is found to be extended by functionally relevant, often flexible stretches, but whether such elongations are present and crucial for the versatileArid5afunctions is unknown. We here provide a near-complete NMR backbone resonance assignment of theArid5aARID domain with N- and C-terminal extensions, which serves as a basis for further studies of its nucleic acid-binding preferences and targeted inhibition by means of NMR. Our data thus significantly contribute to unravelling mechanisms ofArid5a-mediated gene regulation and diseases.