A filamentous scaffold for gene regulation

Proteins of the Drosophila behaviour/human splicing (DBHS) family are involved in many aspects of gene regulation and maintenance like transcription, splicing and DNA repair. The three known members of this family in humans, Non-POU domain-containing octamer-binding protein (NONO), splicing factor proline/glutamine rich (SFPQ), and paraspeckle protein component 1 (PSPC1), form homo- and heterodimers to fulfil these functions by mediating contacts between RNA, DNA, and other protein factors. The dimers can further dynamically oligomerise through α-helical coiled-coils to larger aggregates, which is crucial for many functions of DBHS proteins. While the atomic structures of the dimers are established, the native arrangement in higher oligomers was unknown. Here we present the structure of a filamentous NONO/SFPQ heterooligomer from Cricetulus griseus resolved by cryo-EM. Globular heterodimer domains are alternating on both sides of a strand that is stabilized by an interdigitating network of coiled-coil interactions. Two of these strands assemble into a double strand with only few interactions between them. The globular domains of SFPQ face the counter strand and form a groove while those of NONO face outwards. The different environments of NONO and SFPQ in the filament provide the basis for a differential functionality.